40 to 50 percent humidity.
Maintaining the correct moisture level in the incubator is also important. Humidity should be 50 to 55 percent. For the last three days of incubation, it should be raised to 65 percent. Eggs should be turned several times a day. Many incubators have an automatic feature to take care of this for you. Humidity. The humidity in the incubator needs to be maintained between 55% and 60% relative humidity. The development of the embryo relies on liquid in the egg evaporating over the incubation period. Too much humidity and the albumen will not dry sufficiently and the developing chick will drown 8. Adjust the humidity levels in the incubator. Humidity should be around 45 to 50 percent throughout incubation, except during the last three days when you will want to raise it to 65 percent. You may need higher or lower humidity levels depending on the type of eggs you wish to hatch.  Humidity should be around 50 to 60 percent throughout incubation, except during the last 3 days when you will want to raise it to 65 percent. You may need higher or lower humidity levels depending on the type of eggs you wish to hatch. Consult your hatchery or the available literature on hatching your species of bird. 1 Humidity: The moisture level in the incubator should be about 50 to 65 percent relative humidity (60 percent is often considered the ideal). 2  Moisture is provided by a pan of water under the egg tray. 3  You can use a wet bulb thermometer or a hygrometer to measure humidity. But my friend s making sure i know stuff before i atually incubate. Ive looked at quite a few sites and they say to incubate chicken eggs at 60 to 65% humidity for the first 18 days and then 19-21 up it to 65 to 70% humidity. when he asked what the humidity level needed to be i replied saying this and he said no.  Temperature: The eggs need to be kept at 99.5 degrees at all times; just one degree higher or lower for a few hours can terminate the embryo. Humidity: 40 to 50 percent humidity must be maintained for the first 18 days; 65 to 75 percent humidity is needed for the final days before hatching. Mothering chicken eggs is not for everyone, but if you think it might be your calling, here’s how to do it. Once a hen lays a clutch of eggs, instincts take over. They constantly fuss over them, adjusting them just so throughout the day and rarely leaving the nest for more than a few minutes. Monitor the humidity in the incubator daily to ensure that you keep it at the right percentage for the chicken eggs to hatch. Increase the humidity during the last three days of incubation to 65 percent, 88 degrees Fahrenheit wet bulb or 99.5 degrees Fahrenheit dry bulb reading. Low air humidity causes eggs to lose moisture. When the egg dries out, the chick sticks to the shell and will not hatch. You can use a wet bulb thermometer to determine the amount of humidity in the air and get humidity by utilizing a pan of water. When raising chickens eggs, this rises to 65% - 70% Relative Humidity for the final 3 days prior to hatching (equivalent to wet bulb thermometer readings of 90°F [32°C] to 93°F [34°C]). The higher humidity levels at this time keep the egg membranes soft and easy for the hatching chickens to escape from.  Eggs should be at a 55% humidity rate through to the 18th day and raised to better than 65% during the final days.Chickens take 21 days from start yo hatch and ducks can take as much as 35 days. 1 person found this useful. Miranda Landry. 
http://www.localharvest.org/blog/26992/entry/what_you_need_to_hatch https://www.incubators.org/quail-egg-incubation.html http://www.wikihow.com/Use-an-Incubator-to-Hatch-Eggs http://www.wikihow.com/Hatch-Chicken-Eggs http://www.backyardchickens.com/t/173803/humidity-level-on-hatching-eggs http://modernfarmer.com/2015/04/how-to-incubate-chicken-eggs/ http://www.ehow.com/how_8282716_can-humidity-hatching-chicken-eggs.html http://www.small-farm-permaculture-and-sustainable-living.com/hatching_chickens.html http://www.answers.com/Q/How_much_heat_does_a_chicken_egg_need_to_hatch
how much humidity do chicken eggs need