1/8 inch is the medium-height mark on a standard tape measure. It appears as a dark tick between each quarter-inch mark. The decimal equivalent is 0.125 inches (3.17 mm).
On the Tape Measure
Count 1 marks of this size from the last full inch line to reach 1/8. On professional colour-coded tapes the dark marks are the medium-height marks between the inch lines.
Conversion Reference
| Fraction | Decimal | Millimetres |
|---|---|---|
| 1/8″ | 0.125″ | 3.17 mm |
| Half of 1/8 | 0.0625″ | 1.59 mm |
Common Woodworking Uses
Standard kerf allowance, bolt head clearance, common trim gaps. The 1/8 mark is common in: standard framing, finish carpentry trim fitting, and cabinet construction tolerances.
Also works for recipe halving — the fraction math is the same. Half of 1/8 cup is 1/16 cup. Use the TapeMath calculator for any fraction arithmetic.
How to find it fast: On the TapeMath visual tape, hover over any mark to see its fraction, decimal, and mm immediately — no counting required.