1=throw distance  
example
number=screen size
test at 10m
resulting image size
Elf lens ratio guide
distance to screen
screen size at 10m
20mm 1 to 0.523
10
5.23
25mm 1 to 0.39
10
3.93
38mm 1 to 0.256
10
2.57
50mm 1 to 0.19
10
1.9
65mm 1 to 0.153
10
1.53
76mm 1 to 0.123
10
1.23
100mm 1 to 0.093
10
0.93