Convert 1/2 Inches to MM - Accurate Calculator
Convert 1/2" to millimeters with high precision
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1/2 inch to mm answer
1/2 inch = 12.7 mm exactly.
Exact conversion: 1/2 × 25.4 = 12.7 mm.
Exact formula
Why 25.4 is exact
A half inch is 0.5 inch, so 0.5 × 25.4 = 12.7 mm. The factor 25.4 is exact; rounding only affects optional displayed decimals.
Common approximation and closest metric size
12.7 mm is the exact and standard value. People may say about 13 mm for mental math, but 13 mm is 0.3 mm larger and should not be treated as exact.
Pipe, fittings, and lumber can use nominal sizes. A 1/2 inch label does not always mean the measured part is exactly 12.7 mm.
Where this size is used
Pipe, fittings, and hardware
1/2 inch appears often in fittings, fasteners, and hardware references. Confirm whether the label is nominal or measured before matching metric parts.
Tape measure midpoint and woodworking
Half-inch marks are common layout references. Use 12.7 mm when translating a measured half-inch spacing into metric notes.
Nearby fraction conversions
Nearby fractions give context: 3/8 inch is 9.525 mm, 5/8 inch is 15.875 mm, and 3/4 inch is 19.05 mm.
🔧 DIY & Hardware
For hardware and DIY projects, 1/2" equals 12.70 mm, which is essential when working with metric tools or international specifications.
⚙️ Engineering & Manufacturing
In engineering contexts, 1/2" converts to 12.700000 mm with high precision for accurate technical specifications.
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Editorial conversion notes
How to use this conversion accurately
Formula
1/2 × 25.4 = 12.7 mm exactly.
Rounding, tolerance, and substitution
1/2 inch = 12.7 mm exactly. Saying 13 mm is mental rounding; 13 mm is 0.3 mm larger. Nominal pipe or fitting labels may not describe an actual 12.7 mm diameter.
Practical use cases
- Check pipe, fitting, and hardware references while distinguishing measured diameter from a nominal trade label.
- Translate a half-inch tape-measure or woodworking layout mark into metric notes.
Comparisons and examples
- 3/8 inch = 9.525 mm; 5/8 inch = 15.875 mm; 3/4 inch = 19.05 mm.
- A 13 mm part is not automatically a substitute for a 1/2-inch part.
Editorial value
Separate mathematical conversion from nominal-size conventions and give a decision-useful fit warning.
Route-specific questions
How many millimeters is 1/2 inch?
1/2 inch is 12.7 mm exactly.
Why can a 1/2-inch pipe differ from 12.7 mm?
Pipe and fitting labels are often nominal trade sizes; check the specified inside and outside diameters.