BME280 Environmental Sensor

Q: What does the BME280 measure?

It measures temperature, relative humidity, and barometric pressure. Pressure can also be used to estimate altitude.

Q: Is BME280 digital or analog?

It is digital. ESP32 reads it over I2C or SPI, not with analogRead().

Q: Is BME280 the same as BMP280?

No. BMP280 measures temperature and pressure only. BME280 adds humidity, although many breakout boards look very similar.

Q: Which is better, BME280 or DHT22?

BME280 is usually chosen for weather projects because it adds pressure and uses I2C. DHT22 is simpler for first humidity lessons but has no pressure reading.

Q: What I2C address does BME280 use?

Most modules use 0x76 or 0x77. The address depends on the SDO pin or breakout board design.

Q: Which ESP32 pins should I use?

Use GPIO21 for SDA and GPIO22 for SCL when following common ESP32 Arduino examples. Match GPIO numbers, not physical pin positions from another board.

Q: Can I use different I2C pins?

Yes. ESP32 can map I2C to other pins, but you must call Wire.begin(SDA, SCL) with the pins you wired.

Q: Does BME280 need pull-up resistors?

I2C needs pull-ups on SDA and SCL. Most breakout boards include them, but bare chips do not.

Q: Can I power BME280 from 5 V?

Only if your breakout board is designed for 5 V input and level shifting. For ESP32 beginners, use 3.3 V.

Q: Can BME280 share I2C with an OLED?

Yes. Connect both devices to the same SDA and SCL lines as long as their I2C addresses are different. BME280 is commonly 0x76 or 0x77, while SSD1306 OLED modules are commonly 0x3C or sometimes 0x3D.

Plain-English Overview

The BME280 is a small I2C environmental sensor. With ESP32 it measures temperature, humidity, and local air pressure over four wires: 3.3 V, GND, SDA, and SCL.

Most ESP32 Arduino examples use GPIO21 for SDA and GPIO22 for SCL, and most BME280 modules answer at I2C address 0x76 or 0x77. Temperature tells you how warm the air is. Humidity tells you how much water vapor is in the air. Pressure tells you how hard the air is pushing on everything around it.

BME280 is different from BMP280, even though breakout boards can look very similar. BMP280 measures temperature and pressure only; BME280 also measures humidity. Use the BME280 for weather stations, room monitors, pressure trend logs, approximate altitude experiments, and OLED dashboards, but do not treat it as a lab-grade weather instrument.

Where You Use It

ESP32 weather station
Indoor climate monitor
Greenhouse environment logger
Barometric pressure trend tracker
Approximate altitude monitor
OLED weather dashboard
Classroom atmosphere experiment
Home automation sensor node

Quick Facts

Measures Temperature, humidity, and barometric pressure
Interface I2C on SDA and SCL
Common address 0x76 or 0x77
ESP32 pins GPIO21 SDA, GPIO22 SCL defaults
BME280 vs BMP280 BME280 adds humidity
Library Adafruit BME280 plus Unified Sensor

How It Works

The BME280 contains three sensing systems inside one chip. Its temperature sensor measures the chip temperature, its humidity sensor responds to water vapor in the air, and its pressure sensor measures tiny deflections caused by atmospheric pressure.

The pressure part is the most interesting engineering idea. Air pressure pushes on a microscopic structure inside the chip. That structure changes electrically when it bends. The BME280 converts that tiny change into a local station-pressure reading measured in pascals or hectopascals. Weather apps often show sea-level adjusted pressure instead, so their numbers may differ from your raw sensor reading.

The raw measurements are not directly useful on their own. Bosch stores calibration constants inside each sensor during manufacturing. The Arduino library reads those constants and uses compensation formulas to turn raw ADC values into temperature, humidity, and pressure.

The ESP32 talks to the BME280 over I2C. SDA carries data and SCL carries the clock. GPIO21 and GPIO22 are common Arduino-ESP32 defaults on classic ESP32 boards, not fixed electrical pins. If your board uses different pins, Wire.begin(SDA, SCL) must match the GPIO numbers you actually wired.

Every I2C device has an address, so the ESP32 can ask the BME280 for data while other devices, such as an SSD1306 OLED display, share the same two wires. BME280 modules commonly use 0x76 or 0x77. SSD1306 OLED modules commonly use 0x3C and sometimes 0x3D, so an I2C scanner is the fastest way to confirm the real bus.

Pressure can also estimate altitude, but altitude is only approximate unless you know the current sea-level pressure for your location. The common 1013.25 hPa value is a standard reference, not a promise about your current weather. For weather projects, pressure trends over time are usually more useful than a single pressure number.

Technical Specifications

Arduino library: Adafruit BME280 Library plus Adafruit Unified Sensor

Specification	Value	Why it matters
Supply voltage	Low-voltage chip; use 3.3 V breakout power with ESP32 unless the exact module documentation says otherwise	Some breakouts add regulators or level shifting and some do not, so 3.3 V is the safest beginner choice.
Temperature range	-40 C to 85 C	Covers indoor rooms, outdoor shaded enclosures, greenhouses, and many classroom experiments.
Temperature accuracy	Typically about +/-1 C	Good for trend monitoring; avoid treating the module as a calibrated thermometer.
Humidity range	0 to 100 percent RH, non-condensing	Lets the same board detect dry rooms, comfortable air, and humid greenhouse conditions without exposing the sensing element to liquid water.
Humidity accuracy	Typically about +/-3 percent RH	Useful for comfort and trends, but not a laboratory humidity reference.
Pressure range	300 to 1100 hPa	Covers normal weather pressure and altitude changes from below sea level to mountain elevations.
Pressure accuracy	About +/-1 hPa absolute, better relative resolution	Relative pressure changes are excellent for weather trend and altitude experiments.
Interface	I2C by default; SPI on some breakout boards	This ESP32 guide uses I2C because it needs only two shared signal wires.
I2C address	0x76 or 0x77	The SDO/address pin decides the address; code must match the actual module.
Default ESP32 I2C pins	SDA GPIO21, SCL GPIO22	These are common Arduino core defaults and match most ESP32 tutorials, but they can be changed in Wire.begin(SDA, SCL).
Pull-up resistors	Usually included on breakout boards	I2C lines need pull-ups; bare sensors need an external circuit, and multiple modules can place pull-ups in parallel.
Current consumption	Very low; depends on sampling mode and oversampling	Good for battery projects when paired with ESP32 deep sleep and low sample rates.
Response behavior	Temperature and humidity change gradually; pressure changes slowly indoors	Environmental sensors should be read as trends, not instant switches.

Pinout

VIN / VCC Power input ESP32 3.3 V Use 3.3 V unless the exact breakout documentation confirms other input support. Do not assume VIN is 5 V tolerant.
GND Ground reference ESP32 GND Ground must be shared with the ESP32 and every other I2C device.
SDA / SDI I2C data ESP32 GPIO21 Bidirectional data line. GPIO21 is the common Arduino-ESP32 default; follow GPIO numbers, not another board's physical layout.
SCL / SCK I2C clock ESP32 GPIO22 Clock line generated by the ESP32 master. GPIO22 is common by default, but Wire.begin() can choose other pins.
SDO Address select or SPI data output Usually left as breakout default On many boards, SDO selects I2C address 0x76 or 0x77. Check your module if scanning fails.
CS / CSB SPI chip select or I2C mode select Usually tied HIGH on I2C breakouts If exposed, keep CS high for I2C mode. Pulling it low selects SPI mode on the chip.

Wiring Diagram

The BME280 breakout uses I2C, so it needs power, ground, data, and clock. The common ESP32 Arduino defaults are GPIO21 for SDA and GPIO22 for SCL, but they are not fixed pins. Your wiring and Wire.begin(SDA, SCL) must agree.

Most breakout boards already include I2C pull-up resistors. If you build with a bare BME280 chip, you must add the correct external circuit and follow the datasheet carefully. Beginners should use a 3.3 V breakout module, keep wires short, and run an I2C scanner when the address is uncertain.

ESP32 DevKit wired to a BME280 sensor over I2C using 3.3 V, GND, GPIO21 SDA, and GPIO22 SCL

1
Unplug the ESP32 USB cable before wiring.
2
Place the BME280 breakout on the breadboard so each pin is in a separate row.
3
Connect VIN or VCC to ESP32 3.3 V unless your exact breakout documentation confirms another safe input.
4
Connect GND to ESP32 GND.
5
Connect SDA or SDI to ESP32 GPIO21, following the GPIO number printed for your board.
6
Connect SCL or SCK to ESP32 GPIO22, following the GPIO number printed for your board.
7
Leave SDO and CS at their breakout defaults unless your board documentation says otherwise.
8
Plug in USB, upload the scanner or example code, and confirm whether the module responds at 0x76 or 0x77.

Code Examples

Use the same wiring with Arduino IDE, PlatformIO, or ESP-IDF. Start with Arduino, then graduate when you need a larger project structure.

bme280_esp32_environment_test.ino

#include <Wire.h>
#include <Adafruit_Sensor.h>
#include <Adafruit_BME280.h>

// ESP32 Arduino default I2C pins.
#define I2C_SDA 21
#define I2C_SCL 22

// Standard sea-level pressure, not necessarily today's local sea-level pressure.
// Update this value for better altitude estimates.
#define SEALEVELPRESSURE_HPA 1013.25

const unsigned long READ_INTERVAL_MS = 1000;

Adafruit_BME280 bme;
unsigned long lastReadTime = 0;
bool sensorReady = false;

bool beginBME280() {
  if (bme.begin(0x76)) {
    Serial.println("BME280 found at I2C address 0x76");
    return true;
  }

  if (bme.begin(0x77)) {
    Serial.println("BME280 found at I2C address 0x77");
    return true;
  }

  return false;
}

void setup() {
  Serial.begin(115200);
  delay(1000);

  Wire.begin(I2C_SDA, I2C_SCL);

  Serial.println("BME280 ESP32 environmental sensor test");
  sensorReady = beginBME280();

  if (!sensorReady) {
    Serial.println("BME280 not found at 0x76 or 0x77.");
    Serial.println("Check 3.3 V, GND, SDA=GPIO21, SCL=GPIO22, module address, and run an I2C scanner.");
  }
}

void loop() {
  if (!sensorReady) {
    delay(2000);
    return;
  }

  if (millis() - lastReadTime < READ_INTERVAL_MS) {
    return;
  }
  lastReadTime = millis();

  float temperatureC = bme.readTemperature();
  float humidity = bme.readHumidity();
  float pressureHpa = bme.readPressure() / 100.0F;
  float altitudeM = bme.readAltitude(SEALEVELPRESSURE_HPA);

  if (isnan(temperatureC) || isnan(humidity) || isnan(pressureHpa)) {
    Serial.println("Read failed: check I2C wiring, address, and power.");
    return;
  }

  Serial.print("Temperature: ");
  Serial.print(temperatureC, 1);
  Serial.print(" C  |  Humidity: ");
  Serial.print(humidity, 1);
  Serial.print(" %  |  Pressure: ");
  Serial.print(pressureHpa, 1);
  Serial.print(" hPa  |  Altitude estimate: ");
  Serial.print(altitudeM, 1);
  Serial.println(" m");
}

src/main.cpp

#include <Arduino.h>
#include <Wire.h>
#include <Adafruit_Sensor.h>
#include <Adafruit_BME280.h>

// ESP32 Arduino default I2C pins.
#define I2C_SDA 21
#define I2C_SCL 22

// Standard sea-level pressure, not necessarily today's local sea-level pressure.
// Update this value for better altitude estimates.
#define SEALEVELPRESSURE_HPA 1013.25

const unsigned long READ_INTERVAL_MS = 1000;

Adafruit_BME280 bme;
unsigned long lastReadTime = 0;
bool sensorReady = false;

bool beginBME280() {
  if (bme.begin(0x76)) {
    Serial.println("BME280 found at I2C address 0x76");
    return true;
  }

  if (bme.begin(0x77)) {
    Serial.println("BME280 found at I2C address 0x77");
    return true;
  }

  return false;
}

void setup() {
  Serial.begin(115200);
  delay(1000);

  Wire.begin(I2C_SDA, I2C_SCL);

  Serial.println("BME280 ESP32 environmental sensor test");
  sensorReady = beginBME280();

  if (!sensorReady) {
    Serial.println("BME280 not found at 0x76 or 0x77.");
    Serial.println("Check 3.3 V, GND, SDA=GPIO21, SCL=GPIO22, module address, and run an I2C scanner.");
  }
}

void loop() {
  if (!sensorReady) {
    delay(2000);
    return;
  }

  if (millis() - lastReadTime < READ_INTERVAL_MS) {
    return;
  }
  lastReadTime = millis();

  float temperatureC = bme.readTemperature();
  float humidity = bme.readHumidity();
  float pressureHpa = bme.readPressure() / 100.0F;
  float altitudeM = bme.readAltitude(SEALEVELPRESSURE_HPA);

  if (isnan(temperatureC) || isnan(humidity) || isnan(pressureHpa)) {
    Serial.println("Read failed: check I2C wiring, address, and power.");
    return;
  }

  Serial.print("Temperature: ");
  Serial.print(temperatureC, 1);
  Serial.print(" C  |  Humidity: ");
  Serial.print(humidity, 1);
  Serial.print(" %  |  Pressure: ");
  Serial.print(pressureHpa, 1);
  Serial.print(" hPa  |  Altitude estimate: ");
  Serial.print(altitudeM, 1);
  Serial.println(" m");
}

main/main.c

// ESP-IDF starter structure for this component.
// Keep the wiring from the pinout section, then move the read/write logic into app_main().

#include <stdio.h>
#include "freertos/FreeRTOS.h"
#include "freertos/task.h"

void app_main(void) {
  printf("BME280 Environmental Sensor ready\n");
  while (true) {
    // Add component read/write code here.
    vTaskDelay(pdMS_TO_TICKS(1000));
  }
}

Wire.h starts the ESP32 I2C bus on GPIO21 and GPIO22. Adafruit_BME280 gives your sketch access to compensated temperature, humidity, and pressure readings.

setup() starts Serial Monitor, starts I2C, and tries both common BME280 addresses. If the sensor is not found, the code prints practical wiring checks instead of failing silently.

loop() reads the sensor once per second using millis(). Pressure is divided by 100 because the library returns pascals and weather reports usually use hectopascals. The altitude value is an estimate based on a standard sea-level pressure; it is useful for experiments, not precise navigation.

Expected Output

Open Serial Monitor at 115200 baud. A working BME280 usually prints the detected I2C address first:

BME280 found at I2C address 0x76

Then it prints one reading about every second:

Temperature: 24.1 C | Humidity: 48.7 % | Pressure: 1012.6 hPa | Altitude estimate: 5.4 m

Humidity may rise if you breathe near the board. Temperature changes slowly because the chip and breakout board need time to settle. Pressure usually changes slowly indoors, so watch its trend over minutes or hours.

The pressure value printed here is local station pressure. A weather app may show sea-level adjusted pressure, so a difference can be normal. The altitude value is an estimate based on the reference pressure in the sketch, not a GPS or survey measurement.

Common Mistakes

Swapping SDA and SCL.
Using 0x76 in code when the module is actually 0x77.
Assuming VIN means every breakout is 5 V tolerant.
Forgetting that I2C requires common ground.
Treating GPIO21 and GPIO22 as fixed pins instead of common Arduino defaults.
Comparing raw local pressure directly with sea-level adjusted weather app pressure.
Treating calculated altitude as GPS-level accuracy.
Assuming invalid humidity always proves the board is a BMP280.
Connecting an OLED and BME280 without checking both I2C addresses.
Placing the sensor next to a warm voltage regulator, USB chip, OLED display, direct sun, or enclosed warm board.
Using long jumper wires without understanding I2C pull-ups.

Troubleshooting

Problem	Possible cause	Solution
Serial Monitor says "BME280 not found"	Wrong I2C address, SDA/SCL swapped, no 3.3 V power, no shared ground, wrong bus pins, or a module fault.	Check 3.3 V and GND, confirm SDA on GPIO21 and SCL on GPIO22, try both 0x76 and 0x77, and run an I2C scanner.
I2C scanner shows no devices	Sensor is unpowered, GND is not shared, SDA/SCL are on the wrong ESP32 pins, or the module is damaged.	Measure 3.3 V at the module, confirm GPIO21/GPIO22, and test with short wires.
I2C scanner shows 0x76 or 0x77 but the sketch still fails	The sketch may be using different SDA/SCL pins, a different Wire bus, the wrong library, or loose wiring.	Confirm Wire.begin(21, 22) matches the breadboard, use Adafruit_BME280, and test with short jumper wires.
Humidity is missing, invalid, or unrealistic	You may have a BMP280, the wrong library or sensor object, failed initialization, wiring trouble, or a moisture-contaminated sensor.	Confirm the board is BME280, check that initialization succeeds, rerun the scanner, and remember that BMP280 measures temperature and pressure only.
Temperature reads too high	Heat from the ESP32 board, voltage regulator, USB chip, OLED display, enclosure, direct sun, your fingers, or your breath warms the module.	Move the sensor away from electronics, allow airflow, avoid touching the board, shade it from sun, and let it stabilize.
Pressure seems different from weather websites	Weather reports often show sea-level adjusted pressure, while the sensor measures local station pressure.	Compare trends or apply sea-level correction for your altitude.
Altitude estimate is wrong	Altitude calculation depends on current sea-level pressure, which changes with weather.	Update SEALEVELPRESSURE_HPA from a local weather source or use altitude only for relative experiments.
Readings are noisy	Loose wiring, long I2C lines, weak pull-ups, or airflow/heat around the sensor.	Shorten wires, secure connections, keep the sensor away from heat, and average readings if needed.
ESP32 resets when Wi-Fi starts	USB power is weak or wiring causes voltage dips.	Use a reliable USB cable and power supply; keep sensor power wiring solid.
OLED works but BME280 does not	The BME280 may be at a different address, wired to the wrong bus, using swapped SDA/SCL, or affected by bus pull-up issues.	Run an I2C scanner with both devices connected. Expect BME280 at 0x76 or 0x77 and SSD1306 OLED commonly at 0x3C or sometimes 0x3D.
BME280 works alone but fails with another I2C device	Bus wiring is too long, pull-ups are too strong/weak, or two devices share the same address.	Shorten wires, check addresses, and avoid stacking many pull-up resistors on one bus.
Code will not compile	Missing Adafruit BME280 or Adafruit Unified Sensor library.	Install both libraries from Arduino Library Manager and restart Arduino IDE if needed.
Output appears as unreadable characters	Serial Monitor baud rate does not match Serial.begin(115200).	Set Serial Monitor to 115200 baud.
Sensor fails after being touched or exposed to moisture	Static discharge, condensation, or contamination can affect the sensing element.	Remove power, let the module dry in clean airflow, and replace it if readings remain unrealistic. Do not heat or wash the sensor.
SPI pins are confusing	Some breakout boards expose both I2C and SPI labels.	For this guide, use I2C only: VCC, GND, SDA/SDI, and SCL/SCK. Leave CS/SDO at breakout defaults.

Related Guides

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FAQ

What does the BME280 measure?

Is BME280 digital or analog?

Is BME280 the same as BMP280?

Which is better, BME280 or DHT22?

What I2C address does BME280 use?

Which ESP32 pins should I use?

Can I use different I2C pins?

Does BME280 need pull-up resistors?

Can I power BME280 from 5 V?

Can BME280 share I2C with an OLED?

Why does my scanner show 0x76 but the code fails?

Why is pressure not exactly 1013 hPa?

Why is altitude wrong?

Can BME280 predict rain?

How often should I read BME280?

Is BME280 good for battery projects?

Can BME280 be used outdoors?

Why does humidity respond slowly?

Can I use BME280 with MicroPython?

Does BME280 measure air quality?

Is the BME280 waterproof?

Why do I see heat from the ESP32 in readings?

Glossary - What does BME280 Environmental Sensor mean in an ESP32 project?

Glossary - What is a signal pin?

Parent tips - Is BME280 Environmental Sensor safe for a beginner?

Parent tips - What should I watch during the build?

Teacher tips - How can BME280 Environmental Sensor fit into a classroom lesson?

Teacher tips - How should students be assessed?

Challenge yourself - What is a useful next step after BME280 Environmental Sensor works?

Challenge yourself - How can I prove I understand it?

Mini quiz - What should you check before changing wires?

Mini quiz - Why is common ground important?

Review, Testing, and References

Author: Abdul Mubeen and the ESP32 Engine editorial team. Last updated: 2026-07-05. Reviewed: wiring, code, beginner safety, and ESP32 compatibility. Educational level: Beginner.

Use this component page as an educational starting point. Check official documentation before using the part in production, high-current, outdoor, battery, or safety-critical hardware.

Downloads

Official Bosch BME280 datasheet for electrical limits, calibration behavior, I2C/SPI protocol, and measurement accuracy.

Download Datasheet (PDF)

00Plain-English Overview

AWhere You Use It

01Quick Facts

How It Works

02Technical Specifications

03Pinout

04Wiring Diagram

05Code Examples

OKExpected Output

!Common Mistakes

06Troubleshooting

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