
Here is how to convert 509.5 mm to inches. We will give you the fractional answer, the decimal answer, and illustrate the answer on our tape measure.
One millimeter is equal to 5/127 inches, and 509.5 as a fraction is 1019/2. Therefore, to get the fractional answer to 509.5 mm in inches, we multiply 1019/2 by 5/127 and simplify if necessary.
cm × 5/127 = inches
1019/2 × 5/127 = inches
1019/2 × 5/127 = 20 15/254
1019/2 mm = 20 15/254 inches
509.5 mm = 20 15/254 inches
As promised above, we also have the answer to 509.5 mm in inches in decimal form. Although the fractional answer above is exact, the decimal answer may be rounded if necessary:
20 15/254 ≈ 20.0590551181102
20 15/254 ≈ 20.05906
509.5 mm ≈ 20.05906 inches
Our image below shows 509.5 mm on a tape measure. The top row of the tape measure is inches, and each mark on the bottom row is 1 millimeter (10 millimeter marks equal 1 centimeter).

As you can see, we drew a red line where 509.5 mm and 20.05906 inches meet on the measuring tape.
Millimeters to Inches Calculator
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