An inch ruler with 1/16 marks
This page opens the online ruler in inches. Each long mark with a number is a whole inch. The mark in the middle is 1/2 inch and carries a small "½" label. Shorter marks show 1/4, 1/8 and 1/16.
Pull a guide out of the ruler to mark the end of your object. The tool rounds the length to the nearest 1/16 and shows it as a reduced fraction, such as "3 5/8 in". It also shows the decimal value (3.625 in) and the millimeter value, so you can copy the form you need.
Calibrate first. A card is 3 3/8 in wide and 2 1/8 in tall, which is a good check on the ruler once you have calibrated it.
How to read inch fractions
Count the small marks after the last whole inch. There are 16 steps in an inch. Reduce the fraction by dividing both numbers by 2 until you cannot go further:
- 8 steps is 8/16, which is 1/2.
- 4 steps is 4/16, which is 1/4. 12 steps is 3/4.
- 2 steps is 2/16, which is 1/8. 6 steps is 3/8.
- Odd counts, such as 1, 3 or 11, stay in sixteenths: 11/16.
Add the whole inches in front. If the last whole inch is 3 and you count 10 steps, the length is 3 and 10/16, which is 3 5/8 in.
| Fraction | Decimal (in) | Millimeters |
|---|---|---|
| 1/16 | 0.0625 | 1.59 |
| 1/8 | 0.125 | 3.18 |
| 3/16 | 0.1875 | 4.76 |
| 1/4 | 0.25 | 6.35 |
| 5/16 | 0.3125 | 7.94 |
| 3/8 | 0.375 | 9.53 |
| 7/16 | 0.4375 | 11.11 |
| 1/2 | 0.5 | 12.7 |
| 9/16 | 0.5625 | 14.29 |
| 5/8 | 0.625 | 15.88 |
| 11/16 | 0.6875 | 17.46 |
| 3/4 | 0.75 | 19.05 |
| 13/16 | 0.8125 | 20.64 |
| 7/8 | 0.875 | 22.23 |
| 15/16 | 0.9375 | 23.81 |
| 1 | 1 | 25.4 |
Inches in everyday US sizes
Many US sizes use inches: lumber and hardware, paper, frames, screens and clothing. A US Letter sheet is 8.5 by 11 in. A credit card is 3 3/8 by 2 1/8 in. A US quarter is 24.26 mm across, which is about 0.955 in (the US Mint lists 0.955 in).
When a plan lists a size as a decimal, such as 2.375 in, use the table to find the nearest 1/16. 2.375 in is 2 3/8 in. If you work in metric, the cm ruler uses the same calibration.
Tips for accurate readings
- Look straight down at the edge you read. A sideways view shifts the mark.
- Keep the object flat against the glass.
- Turn snap on to make guides jump to the nearest 1/16.
- Use full screen (F) to give the ruler the whole display.
- Check the result with a coin after you calibrate. If it does not fit, calibrate again.
Inch fractions at a glance
The ruler marks every 1/16 inch. The mark length tells you the fraction. The longest mark between two numbers is 1/2. The next length is 1/4 and 3/4. Then 1/8, 3/8, 5/8 and 7/8. The shortest marks are the odd sixteenths.
A quick way to read a fraction: count the marks past the last whole inch, and write the count over 16. If the count is even, halve both numbers until the count is odd. Six marks past 2 inches is 6/16, which is 3/8, so the length is 2 3/8 in.
Many tape measures stop at 1/16, and so does this tool. If a plan asks for 1/32, use the decimal value from the readout and convert it with the chart on this page.
Measuring common household things
- Picture frames and prints. Standard print sizes are whole inches, such as 4 x 6 and 5 x 7. Check that your print fits the mat opening, which is usually a little smaller.
- Hardware. Bolts, nuts and washers use fractions of an inch. A 1/4 inch bolt has a shaft 6.35 mm wide. Lay it on the screen and read the width with two guides.
- Lumber. A board sold as 2 x 4 is smaller than its name. The finished size in the US is 1 1/2 by 3 1/2 inches. Measure the actual piece when it matters.
- Crafts. Quilt squares, beads and ribbon are often given in inches and sixteenths.
Inches and millimeters together
Some jobs use both units. A part may be drawn in inches but sold in millimeters. Choose the "cm + in" view on the main ruler to see both scales along the same edge. The readout also gives the millimeter value for every guide, so you can copy the unit the other person needs.