MM → Inches
100 mm to inches
100 millimeters equals 3.937008 inches — or about 3 15/16" (nearest 1/16″).
Decimal
3.937 in
Fraction
3 15/16"
Centimeters
10 cm
Feet
0.3281 ft
mm
3.937008
in≈ 3 15/16" (nearest 1/16)
1 in = 25.4 mm · tolerance ±0.0001
Formula
To convert mm to inches, divide by 25.4:
inches = mm ÷ 25.4
inches = 100 ÷ 25.4 = 3.937008
Why 100 mm = 3.937 in
Since 1 inch is defined as exactly 25.4 millimeters, 100 mm converts to 3.937008 inches. Rounded to the nearest 1/16″ that's 3 15/16", which is what you'd read off a standard imperial ruler.