How to Calibrate My Humidity Hygrometer at Home

Calibrate your hygrometer when you take it out of the box.

A hygrometer is used to test humidity levels in a room. They are ideal for monitoring the conditions for plants, reptiles or other humidity-loving organisms. Before your hygrometer leaves the factory, it is set correctly. But during shipment or storage at the store, its calibration may be knocked off. Before you use your hygrometer, it's a good idea to test it's calibration to make sure it is measuring humidity correctly.

Things You'll Need

• Large plastic or glass container
• Lid
• Plastic bottle cap
• Salt

Instructions

1. Fill a bottle cap with salt.

2. Add a few drops of water to the bottle cap. You need just enough to dampen the salt. Don't soak it.

3. Check the hygrometer. It should be within the 40 to 80 percent range. If it is much higher or lower, the hygrometer is probably malfunctioning.

4. Place the salt in a large plastic or glass container.

5. Place the hygrometer in the container.

6. Place the lid on the container to seal it. If you have doubts about whether or not the seal is airtight, tape the lid shut. Or place the container in a sealed clear plastic freezer bag.

7. Leave the container in a cool dry place, undisturbed for 7 hours.

8. Check the hygrometer's reading. It should read 75 percent. If not, record the percentage that it deviates. For example, if the hygrometer's reading is 81 percent, then your hygrometer reads 6 percent too high. Keep this deviation in mind when using the hygrometer. Or, if possible, change the hygrometer's dial to read 6 points lower according to the manufacturer's instructions. This may not be possible on some hygrometers.

9. Re-test your hygrometer annually.

References

• Hermit Crab Association: How do I Calibrate my Hygrometer?
• "Temperature and Humidity Measurement"; Robin E. Bentley; 1998