Temperature and humidity explained

The two numbers that make or break a hatch.

1. 1

   Forced-air incubators: 37.5°C. Still-air: 38.5°C at the top of the eggs.

2. 2

   Use a separate calibrated thermometer/hygrometer — built-in sensors drift.

3. 3

   Humidity too high early causes big, wet chicks that drown at hatch; too low causes shrink-wrapping. Aim for a 13% weight loss by day 18.

4. 4

   Adjust humidity with surface area of water, not depth.