MM → Inches
31.8 mm to inches
31.8 millimeters equals 1.251969 inches — or about 1 1/4" (nearest 1/16″).
Decimal
1.252 in
Fraction
1 1/4"
Centimeters
3.18 cm
Feet
0.1043 ft
mm
1.251969
in≈ 1 1/4" (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 = 31.8 ÷ 25.4 = 1.251969
Why 31.8 mm = 1.252 in
Since 1 inch is defined as exactly 25.4 millimeters, 31.8 mm converts to 1.251969 inches. Rounded to the nearest 1/16″ that's 1 1/4", which is what you'd read off a standard imperial ruler.