millimeter	decimal inch	closest fractional inch
5mm	0.20"	1/5"
6mm	0.24"	1/4"
8mm	0.31"	5/16"
10mm	0.39"	between 3/8 & 7/16"
12mm	0.47"	between 7/16 & 1/2"
14mm	0.55"	between 1/2 & 9/16"
16mm	0.63"	5/8"
18mm	0.71"	between 5/8 & 3/4"  (diameter of a US dime, a penny is 19mm))
20mm	0.79"	between 3/4 & 13/16"
22mm	0.87"	7/8"    (a US nickel is 21mm)
24mm	0.95"	between 15/16 & 1"  (diameter of a US quarter)
25mm	0.98"	hair under 1"
26mm	1.02"	hair over 1"
28mm	1.10"	1-1/8"
30mm	1.18"	1-3/16"  (the diameter of a US half dollar is 30.61mm)
32mm	1.26"	1-1/4"
34mm	1.34"	1-1/3"
35mm	1.38"	1-3/8"
36mm	1.42"	1-7/16"
38mm	1.50"	1-1/2"
40mm	1.57"	1-9/16"  (a golf ball is about 43mm, 1.68" in diameter)
45mm	1.77"	1-3/4"
49mm	1.93"	1-15/16"
50mm	1.97"	2"
55mm	2.16"	2-1/8"
60mm	2.36"	2-1/3"
63mm	2.48"	2-1/2"
65mm	2.56"	2-9/16"
67mm	2.64"	2-5/8"  (size of a tennis ball)
70mm	2.75	2-3/4"
76mm	3"	3"       (an average base ball is about 74mm)
80mm	3.15"	3-1/8"
90mm	3.54"	3-1/2"
100mm	3.94"	4"     (the diameter of a soft ball avg's 3.5-3.8" unless you're in Chicago)
110mm	4.33"	4-1/3"
120mm	4.72"	4-3/4"
1000mm  (1 meter)	39.37	39-3/8"