Measure from the underside of the top metal shelf. If your not going to put a large number in this bator at once,then inside space is not an issue for you,but by removing the inside plastic tray on the door,this will alow the egg trays to be bigger,but it's not necessary if your only wanting to hatch 20 or so eggs at a time. My homemade bator will hold about 450 chicken eggs at a time with all 3 trays full.