MM → Inches
21.5 mm to inches
21.5 millimeters equals 0.846457 inches — or about 7/8" (nearest 1/16″).
Decimal
0.8465 in
Fraction
7/8"
Centimeters
2.15 cm
Feet
0.0705 ft
mm
0.846457
in≈ 7/8" (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 = 21.5 ÷ 25.4 = 0.846457
Why 21.5 mm = 0.8465 in
Since 1 inch is defined as exactly 25.4 millimeters, 21.5 mm converts to 0.846457 inches. Rounded to the nearest 1/16″ that's 7/8", which is what you'd read off a standard imperial ruler.