How do I calibrate my hygrometer?

Hatching fertile eggs can be such a fun adventure! To increase your chance of a successful hatch, you may want to plan ahead and calibrate your hygrometer/thermometer. One of the most common problems during hatching is incorrect humidity and temperature in the incubator. Even a new hygrometer may not be properly calibrated, so it is better to check your equipment before starting a batch of eggs.

To calibrate your hygrometer:

Mix 1/2 cup of salt and 1/4 cup of water in a coffee cup or other small container. It will be a thick mixture.

Put your thermometer/hygrometer into a large zip-close plastic bag with the container of salt mixture and close the bag completely.

Leave the bag undisturbed at room temperature overnight. Be careful not to let the water touch the hygrometer.

The next morning, if the the relative humidity in the bag measures 75%, your hygrometer is properly calibrated. Be sure to read the measurement while the hygrometer is still inside the bag. Removing the hygrometer from the bag before you take your reading will cause the measurement to change.

If the humidity is higher or lower than 75%, be sure to make note of the difference, so that you can add or subtract the difference during incubation. For example, if the hygrometer reads the humidity in the bag as 71%, then be sure to add 4% to your readings during incubation. (75% - 71% = 4% reading deviation)