MM → Inches
8.1 mm to inches
8.1 millimeters equals 0.318898 inches — or about 5/16" (nearest 1/16″).
Decimal
0.3189 in
Fraction
5/16"
Centimeters
0.81 cm
Feet
0.0266 ft
mm
0.318898
in≈ 5/16" (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 = 8.1 ÷ 25.4 = 0.318898
Why 8.1 mm = 0.3189 in
Since 1 inch is defined as exactly 25.4 millimeters, 8.1 mm converts to 0.318898 inches. Rounded to the nearest 1/16″ that's 5/16", which is what you'd read off a standard imperial ruler.