Incubator humidity converter

The chart

Wet-bulb reading in °F for each relative humidity, by incubator (dry-bulb) temperature, as printed in Mississippi State's and Minnesota's bulletins. Kentucky prints a 99.5°F row that agrees with the values between them.

The species settings on the incubation calculator already show both units.

Common questions

Why do incubation tables give humidity as a temperature?

Because that is what a wet-bulb thermometer reads. Mississippi State's bulletin explains that most of the incubator industry refers to humidity as degrees Fahrenheit wet-bulb rather than percent relative humidity, that the two are interconvertible, and that the actual humidity depends on the dry-bulb temperature too. Modern tabletop incubators report percent, so the chart is the bridge between the extension tables and your display.

What humidity should a chicken incubator run at?

Mississippi State's table gives 85 to 87°F wet-bulb until lockdown and 90°F for the hatch, which at a 100°F dry-bulb converts to about 54 to 59 percent and about 68 percent relative humidity. Minnesota gives 50 to 55 percent, rising to about 65 percent for the last three days. Your incubator's manual wins where it differs, and the air cell at candling is the final check.

The converter only covers 99 to 102°F and 45 to 70 percent. Why?

Those are the limits of the published extension chart. Inside them the converter interpolates between the printed values; outside them it extends the nearest step of the chart in a straight line, so treat readings beyond the edges as rough.

1. Care and Incubation of Hatching Eggs. Dr. Tom W. Smith, Mississippi State University, Poultry Science.
2. Hatching and Brooding Small Numbers of Chicks (AG-FO-0631). Melvin L. Hamre, Minnesota Extension Service, University of Minnesota. Reviewed 1990.
3. Development of the Chick (ASC-195). Tony Pescatore and Jacquie Jacob, University of Kentucky Cooperative Extension. December 2012.

We read each document ourselves and last checked this page against them on October 5, 2026. Where they disagree, we show you the disagreement instead of picking a winner quietly.