8 mm to Inches
Convert 8 millimeters to inches — instant, accurate, and easy
The Answer
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How to Convert 8 mm to Inches
To convert 8 millimeters to inches, divide the millimeter value by 25.4. This is because one inch equals exactly 25.4 millimeters — a standard defined by international agreement.
The Calculation
Applying the formula to 8 mm:
Result Summary for 8 mm
- Decimal inches: 0.3150″
- Fractional inches: 5/16″ (nearest 1/64)
- Feet and inches: 0 ft 0.31 in
8 mm Compared With 5/16 Inch
8 mm is approximately 0.315 inches. The nearest 1/16-inch mark is 5/16 inch (7.9375 mm), 0.0625 mm below 8 mm.
Because the difference is only about 0.06 mm, 8 mm and 5/16-inch wrenches usually fit each other’s fasteners. An M8 bolt has a nominal major diameter of 8 mm; its hex head is normally 13 mm across the flats.
Reference Table — Values Near 8 mm
| Millimeters | Decimal Inches | Fractional Inches |
|---|---|---|
| 5 mm | 0.1969″ | 13/64″ |
| 6 mm | 0.2362″ | 15/64″ |
| 7 mm | 0.2756″ | 9/32″ |
| 8 mm | 0.3150″ | 5/16″ |
| 9 mm | 0.3543″ | 23/64″ |
| 10 mm | 0.3937″ | 25/64″ |
| 11 mm | 0.4331″ | 7/16″ |
8 mm in Other Units
Millimeters convert cleanly into every other length unit. Here is 8 mm expressed seven different ways — useful when a drawing, spec sheet or supplier quotes a unit other than inches.
| Unit | 8 mm equals |
|---|---|
| Centimeters (cm) | 0.8 cm |
| Meters (m) | 0.008 m |
| Inches (in) | 0.3150 in |
| Feet (ft) | 0.0262 ft |
| Yards (yd) | 0.00875 yd |
| Thousandths of an inch (mil) | 315 mil |
| Typographic points (1/72 in) | 22.68 pt |
How Accurate Is Each Fraction of 8 mm?
8 mm equals 0.3150″ (rounded to four decimal places). Any fraction is a further rounding of the full-precision value, so each one carries a small error. This table shows the closest fraction at each common denominator and how far it actually sits from 8 mm.
| Rounded to | Fraction | Decimal | Fraction vs. original |
|---|---|---|---|
| Nearest 1/2″ | 1/2″ | 0.5000″ | +4.700 mm (above original) |
| Nearest 1/4″ | 1/4″ | 0.2500″ | −1.650 mm (below original) |
| Nearest 1/8″ | 3/8″ | 0.3750″ | +1.525 mm (above original) |
| Nearest 1/16″ | 5/16″ | 0.3125″ | −0.063 mm (below original) |
| Nearest 1/32″ | 5/16″ | 0.3125″ | −0.063 mm (below original) |
| Nearest 1/64″ | 5/16″ | 0.3125″ | −0.063 mm (below original) |
For woodworking, DIY and general workshop use, 5/16″ is the practical choice — it lands within 0.4 mm of 8 mm. For machining, toolmaking or CAD, use the decimal value 0.3150″ rather than any fraction.
FAQ About 8 mm to Inches
How many inches is 8 mm?
8 millimeters equals 0.3150 inches (rounded to 4 decimal places), or approximately 5/16″ (nearest 1/64 inch).
How accurate is the 8 mm to inches conversion?
The conversion of 8 mm to 0.3150 inches uses the exact definition 1 inch = 25.4 millimeters; the four-decimal result is rounded, so it is approximate.
Can I convert 8 mm to feet?
Yes. 8 millimeters equals approximately 0 ft 0.31 in.
📏 Need to measure 8mm accurately?
Digital calipers typically display readings to 0.01 mm resolution, enough to check 8 mm (≈ 0.3150″). See current options:
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