3/8 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 0.375 inches (9.52 mm).
On the Tape Measure
Count 3 marks of this size from the last full inch line to reach 3/8. On professional colour-coded tapes the dark marks are the medium-height marks between the inch lines.
Conversion Reference
| Fraction | Decimal | Millimetres |
|---|---|---|
| 3/8″ | 0.375″ | 9.52 mm |
| Half of 3/8 | 0.1875″ | 4.76 mm |
Common Woodworking Uses
Standard kerf allowance, bolt head clearance, common trim gaps. The 3/8 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 3/8 cup is 3/16 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.