Testing Various Low-Cost Hygrometers

See also the companion page on thermometers.

Described here are my own experiences assessing accuracy and calibrating the following devices. Results only represent my own specific devices which I have bought from various retail sources.

Bosch Sensortec BME280
Measurement Specialties HTU21D
Silicon Labs Si7021
Sensirion SHT71, SHT31
Aosong DHT11, DHT22, AM2302, AM2320, AM2321

I would like to stress here that my interest in this is rather more about the methodolgy of testing and how accurately I can set up the calibration experiment using low or zero cost equipment than it is about truly calibrating these sensors. It would be presumptuous of me to suggest I know better than the metrology experts at some of the world's premier digital sensor manufacturers. Where I see a deviation between my measurements and multiple sensors I happily assign the error to my experimental procedure and look for improvements. My setup went through many iterations on that basis. Once I could start to see systematic repeatable differences between sensors, that might be 'error' in one or other of the devices. When reading these pages, please do remember at all times that a discrepancy from prediction could be fault in the sensor or in my test.

These pages have grown over time as I try repetitions and variations on certain experiments. Though I have gone back an updated some of the older write-ups in the light of new results, some results described in the older pages are likely to be outdated. I have therefore split the conclusions into two sections. I have a single page I can keep up-to-date with my latest overview and summary of each sensor. Then I have all the detailed results which present the actual data and detailed discussion presented as they were at the time that web page were written. Comments on those older detailed write-ups could contradict statements I make in my latest overview summary.