BMP388 Altitude Reading Nowhere Near Accurate


Hello, I have purchased a BMP388 from you the other day and have just received it today. I am now testing it and have come across a big problem. Using a simple test script - making sure the sea level pressure is accurate etc. I get an altitude reading of 200m, which is a lot considering the highest point in my county (Norfolk) is 103m and my altitude is about 16m (I think). Could I have received a dodgy sensor or could there be another problem?



Aaah checking several websites for local sea level pressure gives me different results but I am still 15m or so off now. All websites say different to the first very inaccurate one I looked at.


Still about 15 metres off, is this normal?


The closest airports QNH reading should be as good as it gets for atmospheric pressure adjusted to mean sea level.


How are you connecting it (and what to?), which library are you using?

Presuming you’ve seen the Adafruit setup guide, it might be worth asking Adafruit directly- either on their discord server ( or on their own forums.


Okay, thanks for the help all. Now only 5m off - maybe the rain was skewing the figures a bit. I am using the Adafruit Python library. I have already coded a quick script to use an API to get the QNH and it works a treat. No chance of it being completely accurate as weather stations seem to all round their pressure readings to the nearing whole millibar. I will ask on the Adafruit Forums to find out how to optimise accuracy.


Edit - it turns out the API I am using gives double figures, oops


The QNH is what airline pilots use to set thier altimeter in the plan so it “should be” super accurate.
What you get in weather forecasts from a radio station not so much.

I have a couple of weather clocks using a BME680 and Raspberry Pi A+. I’m only interested if the pressure is low or high etc. I don’t bother correcting for sea level and round off my readings to whole numbers. My house is about 90 feet above sea level and the dog park I take my portable to is maybe 20 feet above sea level. Not enough difference for me to worry about for what I use my weather clocks for. If I was wanting accurate altitude readings like you are, it would be a different story.