11 of the 13 features in our table differ between the SCD40 and the MH-Z19C.
CO₂ · temperature · humidity · I²C · 2.4 to 5.5 V
Sensirion’s small photoacoustic CO₂ sensor: ±(50 ppm + 5 %) from 400 to 2,000 ppm, 2.4 to 5.5 V, I²C.
Watch out: Specified only up to 2,000 ppm: for greenhouses or higher levels, choose the SCD41.
CO₂ · UART/PWM · 4.9 to 5.1 V
A low-cost NDIR CO₂ sensor on UART or PWM: it reads from 400 to 5,000 ppm, with ±(50 ppm + 5 %) stated from 400 to 2,000 ppm.
Watch out: It needs 5 V (5.0 ± 0.1 V in Winsen’s table) and draws 125 mA peaks. Self-calibration is on by default and assumes the room reaches 400 ppm every day: turn it off in rooms that are never aired.
| Feature | SCD40 | MH-Z19C |
|---|---|---|
| Measures | CO₂ · temperature · humidity | CO₂ |
| Technology | Photoacoustic NDIR | NDIR (infrared) |
| CO₂ range | 400 to 2,000 ppm | 400 to 5,000 ppm |
| CO₂ accuracy | ±(50 ppm + 5 %) | ±(50 ppm + 5 %), stated up to 2,000 ppm |
| Interface | I²C | UART, PWM |
| I²C address | 0x62 | Not I²C |
| Supply | 2.4 to 5.5 V | 4.9 to 5.1 V |
| Lowest average current | 3.2 mA | 40 mA |
| Warm-up | – | 1 min |
| Rated lifetime | – | 10 years or more |
| ESPHome | scd4x | mhz19 |
Same on both: status.
In our table the MH-Z19C has nothing the SCD40 lacks: choose it for price, availability or a board you already have.
Open the sensor comparison →Tick what your project needs and see which sensor fits best.
SCD40: I²C address, wiring and pull-ups →
The SCD40 offers temperature and humidity readings too, a standard I²C bus shared with other sensors, a 3.3 V supply without a 5 V rail, and a lower average current; in our table the MH-Z19C has no advantage of its own, apart from price or availability.
Both measure real CO₂: ±(50 ppm + 5 %) for the SCD40 (400 to 2,000 ppm), ±(50 ppm + 5 %) for the MH-Z19C (400 to 2,000 ppm).
Not as a drop-in: the SCD40 uses I²C and the MH-Z19C a UART or PWM, so the wiring and the code change. Check the supply too: 2.4 to 5.5 V for the SCD40, 4.9 to 5.1 V for the MH-Z19C.
Figures from the makers’ datasheets and product pages and the ESPHome documentation, checked in November 2026.