Inch Ruler
This inch ruler is marked in sixteenths of an inch with fraction labels, and you can calibrate it with a bank card so one inch is a real inch. Use the quick buttons to see 1 to 6 inches, and check the table that converts inches to centimetres and millimetres.
Step 1. Calibrate once. Hold the object against the screen and move the slider until the outline is exactly as wide as the real thing.
Step 2. Measure. Slide the line along the ruler, or tap a quick button.
Use the inch ruler in three steps
- Calibrate with the card or quarter so that one inch on the screen is one real inch.
- Press Show me 4 in, or any size from 1 to 6, to move the line to that length, or slide it yourself.
- Read the length in inches and in the nearest sixteenth. For clocks and time zones, try time now.
Inches to centimetres and millimetres
One inch is exactly 25.4 millimetres. To change inches to centimetres multiply by 2.54, and to change centimetres to inches divide by 2.54. The table gives common values.
| Inches | Millimetres | Centimetres |
|---|---|---|
| 1/16 in | 1.5875 mm | 0.159 cm |
| 1/8 in | 3.175 mm | 0.318 cm |
| 1/4 in | 6.35 mm | 0.635 cm |
| 1/2 in | 12.7 mm | 1.27 cm |
| 1 in | 25.4 mm | 2.54 cm |
| 2 in | 50.8 mm | 5.08 cm |
| 3 in | 76.2 mm | 7.62 cm |
| 4 in | 101.6 mm | 10.16 cm |
| 6 in | 152.4 mm | 15.24 cm |
| 12 in | 304.8 mm | 30.48 cm |
How big is an inch
If you need a sanity check, compare with things you know. These sizes come from the standards for cards, coins and paper.
| Object | In inches | In millimetres |
|---|---|---|
| Credit card | 3.370 × 2.125 in | 85.60 × 53.98 mm |
| US quarter | 0.955 in across | 24.26 mm |
| US dollar bill | 6.14 × 2.61 in | 155.96 × 66.29 mm |
| A4 paper | 8.27 × 11.69 in | 210 × 297 mm |
| US Letter paper | 8.5 × 11 in | 215.9 × 279.4 mm |
Reading fractions of an inch
An inch ruler divides each inch into 16 parts. The marks get shorter as the fractions get smaller: whole inches are longest, then halves, quarters, eighths and sixteenths. When you read a length, find the last whole inch and count the sixteenth marks past it, then simplify the fraction: 8 sixteenths is a half, 4 sixteenths is a quarter and 12 sixteenths is three quarters.
Limits
Calibration is stored in your browser, and a change of browser zoom or screen needs a new calibration. We checked the ruler in Chrome on a computer and have not yet tested iPhone Safari or Android Chrome. Tell us at [email protected] if it behaves differently on your device.
See the full online ruler for centimetres, millimetres and printing, or go back to OxoApp.
Frequently asked questions
How big is one inch?
One inch is exactly 25.4 millimetres or 2.54 centimetres. That value was fixed in 1959 by an agreement between the US, the UK and other countries. A US quarter is a bit under one inch across, at 0.955 inches.
How do I read the marks on an inch ruler?
The longest mark is a whole inch, the next longest is a half, then quarters, eighths and sixteenths. Count the small marks from the last whole inch. For example, three marks after the 2 is 2 and 3/16 inches.
What is 1/16 of an inch in millimetres?
1/16 inch is 1.5875 millimetres. A 1/8 inch is 3.175 mm and a 1/4 inch is 6.35 mm.
Is the ruler accurate?
Only as accurate as your calibration. Match the outline to a bank card, 3.370 inches wide, and check against a real ruler. It can be off by a millimetre or more.
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