MM → Inches
420 mm to inches
420 millimeters equals 16.535433 inches — or about 16 9/16" (nearest 1/16″).
Decimal
16.5354 in
Fraction
16 9/16"
Centimeters
42 cm
Feet
1.378 ft
mm
16.535433
in≈ 16 9/16" (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 = 420 ÷ 25.4 = 16.535433
Why 420 mm = 16.5354 in
Since 1 inch is defined as exactly 25.4 millimeters, 420 mm converts to 16.535433 inches. Rounded to the nearest 1/16″ that's 16 9/16", which is what you'd read off a standard imperial ruler.