MM → Inches
21 mm to inches
21 millimeters equals 0.826772 inches — or about 13/16" (nearest 1/16″).
Decimal
0.8268 in
Fraction
13/16"
Centimeters
2.1 cm
Feet
0.0689 ft
mm
0.826772
in≈ 13/16" (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 = 21 ÷ 25.4 = 0.826772
Why 21 mm = 0.8268 in
Since 1 inch is defined as exactly 25.4 millimeters, 21 mm converts to 0.826772 inches. Rounded to the nearest 1/16″ that's 13/16", which is what you'd read off a standard imperial ruler.