The online ruler in inches is a free imperial-units ruler that displays inches at true actual size on any screen. Calibrate once with a credit card and the ruler measures within plus or minus 0.02 inch (about 0.5 mm) for all standard fractional and decimal inch readings. Whether you searched for "online ruler inches", "ruler online inches", "inch ruler online", or "online ruler in inches", this is the same calibrated tool.
Tick marks show whole inches plus 1/2, 1/4, 1/8, and 1/16 inch fractional divisions, exactly like a physical wooden or steel ruler. The inch ruler online toggles to decimal mode for engineering or scientific use, and it covers 0 to 12 inches with horizontal scroll to extend up to 20 inches.
Use this online ruler in inches for: US lumber and hardware sizes, sewing patterns, photo print sizes (4 by 6, 5 by 7, 8 by 10), home decor purchases, and any project using imperial units.
How to Use the Online Inch Ruler
- Calibrate once using a standard credit card (3.37 inches or 85.6 mm wide). The calibration applies to all units, not just inches.
- Confirm inch mode is selected via the unit toggle above the ruler. Inches is the default on this page.
- Align your object with the red 0 inch line at the left edge.
- Read fractions by tick mark height: tallest ticks are whole inches, then 1/2, 1/4, 1/8, and 1/16 inch divisions in decreasing height.
When to Use an Online Inch Ruler
- Woodworking and DIY. US lumber and hardware are sized in imperial units. Stud spacing (16 in), 2 by 4 dimensions, plywood thickness.
- Sewing and quilting. Most US patterns use fractional inches like 1/4 inch seam allowances.
- US school work. Math, geometry, and science homework using imperial units.
- Photography and printing. Standard US print sizes (4 by 6, 5 by 7, 8 by 10, 11 by 14, 16 by 20).
- Online shopping in US, UK, and Canada. Product specs often list inches, especially for electronics screen sizes.
- Crafts. Cardstock, ribbon, scrapbooking, and beading materials in inches.
Inch Quick Reference
- 1 inch equals 25.4 mm or 2.54 cm, exact by international definition since 1959
- 1 foot equals 12 inches, 304.8 mm, or 30.48 cm (just over the standard 30 cm ruler)
- 1 yard equals 36 inches, 914.4 mm, or 91.44 cm
- 1/16 inch equals 1.5875 mm, the smallest tick on most rulers
- 1/8 inch equals 3.175 mm
- 1/4 inch equals 6.35 mm
- 1/2 inch equals 12.7 mm
Reading Fractional Inches
Each inch is divided into 16 equal parts on a standard ruler in inches. The trick is recognizing tick height:
- Tallest tick: 1 inch (and half-inch ticks).
- Medium-tall ticks: 1/4 and 3/4 inch positions.
- Shorter ticks: 1/8, 3/8, 5/8, 7/8 inch positions.
- Shortest ticks: 1/16 inch increments between the others.
For a complete fraction reading guide, see how to read a ruler in inches and centimeters.
Common Imperial Sizes to Measure
The online ruler in inches is built around the sizes you most often need to verify:
- Letter paper: 8.5 by 11 inches.
- Legal paper: 8.5 by 14 inches.
- Index cards: 3 by 5 and 4 by 6 inches.
- Photo prints: 4 by 6, 5 by 7, 8 by 10.
- Phone screens: iPhone 15 is 6.1 inch diagonal, iPhone 15 Plus is 6.7 inch.
- Tablet screens: iPad is typically 10.9, 11, 12.9, or 13 inch diagonal.
Need Metric?
For metric measurements, the same tool toggles to online ruler in CM or mm ruler online. The calibration applies to all units, so you only calibrate once.
Get a Credit Card
Grab any standard bank card. Every credit card and debit card worldwide is exactly 85.6 mm wide by ISO/IEC 7810 ID-1 standard.
Click "Calibrate"
The amber Calibrate button sits in the ruler toolbar. Click it to open the calibration overlay on top of the ruler.
Drag to Match
Drag the blue calibration box right edge until its width exactly matches the long edge of your card.
Confirm and Done
Click Confirm. Your screen pixel density is saved to your browser. All future measurements display at real-world actual size.
Width: 85.6 mm (8.56 cm or 3.37 inches) · Height: 53.98 mm (5.4 cm or 2.13 inches)
Every bank card worldwide follows this exact standard.
Unit Conversion Reference
| Centimeters (cm) | Millimeters (mm) | Inches (fraction) | Inches (decimal) |
|---|---|---|---|
| 0.1 cm | 1 mm | 1/16" | 0.0394" |
| 0.5 cm | 5 mm | 3/16" | 0.1969" |
| 1 cm | 10 mm | 3/8" | 0.3937" |
| 2 cm | 20 mm | 13/16" | 0.7874" |
| 2.54 cm | 25.4 mm | 1" | 1.0000" |
| 5 cm | 50 mm | 1 15/16" | 1.9685" |
| 10 cm | 100 mm | 3 15/16" | 3.9370" |
| 15 cm | 150 mm | 5 7/8" | 5.9055" |
| 20 cm | 200 mm | 7 7/8" | 7.8740" |
| 25 cm | 250 mm | 9 13/16" | 9.8425" |
| 30 cm | 300 mm | 11 13/16" | 11.8110" |
| 50 cm | 500 mm | 19 11/16" | 19.6850" |