Inch ruler
The inch remains the everyday unit across the United States — for woodworking, sewing, hardware, and anything sold by the foot. Calibrate your display once, switch the ruler to inches, and read whole inches plus fractions down to a sixteenth.
What is an inch?
An inch is a US customary (imperial) unit defined as exactly 2.54 centimeters. Twelve inches make a foot, 36 make a yard. Unlike metric units, inches are traditionally read as fractions — halves, quarters, eighths, sixteenths — rather than decimals, and the on-screen ruler is drawn exactly that way.
Reading the inch scale
Numbered ticks are whole inches. Between them, tick length encodes the fraction — the longer the tick, the simpler the fraction:
- Longest unnumbered tick — the half inch (½″), one per inch.
- Next longest — quarter inches (¼″, ¾″).
- Medium ticks — eighth inches (⅛″, ⅜″, ⅝″, ⅞″).
- Shortest ticks — sixteenths (1/16″ … 15/16″).
Read from the numbered inch below the object’s end and count forward. Two medium ticks past the 3″ mark is 3 and 2/8 — simplify it to 3¼″. Five of the shortest ticks past 1″ is 1 and 5/16 inches. The full reading method, with worked examples, is in the reading guide.
Fraction ↔ decimal ↔ metric
| Fraction | Decimal (in) | Metric |
|---|---|---|
| 1/16″ | 0.0625 | 1.59 mm |
| ⅛″ | 0.125 | 3.18 mm |
| ¼″ | 0.25 | 6.35 mm |
| ½″ | 0.5 | 12.7 mm |
| 1″ | 1.0 | 25.4 mm (exact) |
When inches beat metric
If the thing you’re measuring was made in inches — lumber dimensions, screw sizes, pipe fittings, US clothing patterns — measure in inches and skip the conversion. A “2×4” stud, a ¼″ bolt, or a 9″ cake pan all have round numbers in inches and awkward ones in metric. Match the ruler to the object’s native unit and the numbers stay friendly.
Frequently asked questions
How many sixteenths are in an inch?
Sixteen. The on-screen inch ruler divides every inch into 16 equal ticks. The 8th tick is the half inch, the 4th and 12th are quarter inches, and the 2nd, 6th, 10th, and 14th are eighth-inch marks.
How many centimeters is an inch?
Exactly 2.54 centimeters, by international definition. One centimeter is about 0.3937 inches.
Why do rulers use fractions instead of decimals?
Tradition and divisibility. Halves, quarters, and eighths come from repeatedly halving an inch, which is easy to do physically and to read by eye. Decimal inches exist too — machinists work in thousandths — but fractional inches remain the standard for everyday US measuring.
Try it on your screen right now
The live ruler is on the home page — calibrated to your display in under a minute.
Open the ruler