How to convert pixels to inches
A pixel has no fixed size of its own. Its size depends on the pixel density: how many pixels fit in each inch, written as PPI (pixels per inch) or, for printing, DPI. The formula is inches = pixels ÷ PPI, and pixels = inches × PPI. A 1200-pixel-wide photo prints 4 inches wide at 300 PPI, or 12.5 inches wide at 96 PPI.
Related guides: Paper Sizes Chart (Inches and Millimeters) · How to Measure a TV or Monitor Screen Size
How to use it
- Type the number of pixels, or type inches to convert the other way.
- Set the pixel density: 300 for good-quality prints, 96 for web and CSS, or your screen's own PPI.
- Read the size in inches, centimeters, millimeters and points.
Good to know
- In CSS, 1 inch is defined as exactly 96 px, whatever the real screen.
- 1 inch = 72 points, the unit used for font sizes in print.
- At 300 PPI one pixel is 0.085 mm wide; at 96 PPI it is 0.265 mm.
- Phone screens pack about 400–500 physical pixels per inch; the iPhone 17 has 460.
Pixels needed for common print sizes
Print size in inches multiplied by the pixel density. 300 PPI is the usual target for photo prints; 150 PPI is fine for posters seen from a distance.
| Print size | At 300 PPI | At 150 PPI |
|---|---|---|
| 4 × 6 in | 1200 × 1800 px | 600 × 900 px |
| 5 × 7 in | 1500 × 2100 px | 750 × 1050 px |
| 8 × 10 in | 2400 × 3000 px | 1200 × 1500 px |
| 8.5 × 11 in (US Letter) | 2550 × 3300 px | 1275 × 1650 px |
| 11 × 14 in | 3300 × 4200 px | 1650 × 2100 px |
| A4 (8.27 × 11.69 in) | 2480 × 3508 px | 1240 × 1754 px |
- To find the largest sharp print from a photo, divide its pixel size by 300: a 4000 × 3000 px photo prints well up to about 13.3 × 10 in.
- Raising the PPI setting in an image editor doesn't add detail. It only changes the print size stored in the file.
Three ways to calibrate
Auto-detect your device
The ruler recognizes about 130 phones, tablets, laptops and monitors, including iPhones, Galaxy phones, Pixels and MacBooks.
Enter your screen size
Enter your screen's diagonal size (for example, 15.6" for a laptop), and the ruler works out the scale from your screen resolution.
Calibrate with a bank card
Hold any bank card against the outline on screen and move the slider until they match. Bank cards are the same size everywhere: 85.60 × 53.98 mm.
How accurate is the ruler?
How accurate the ruler is depends on how well it knows your screen's pixel density, meaning how many pixels fit in an inch. There are three ways to set it, from most to least accurate:
Bank card (±0.5%): Bank and credit cards are made to one worldwide size, 85.60 × 53.98 mm (ISO/IEC 7810 ID-1). Because every card is exactly the same, matching one on screen gives the most accurate result.
Auto-detect (±1%): The ruler looks up your device's published screen size and resolution. Screens of the same model can differ very slightly, so this is a little less exact. It covers about 130 devices.
Screen size (±2%): You type in your screen size, and the ruler works out the rest from your resolution. Advertised sizes are rounded (a "15.6-inch" screen may really be 15.59 inches), so this is the least exact method. It's a good fallback when you don't have a card.
Real-life objects to check your measurements
Use these everyday objects to confirm the ruler is calibrated correctly.
Bank or credit card: 85.60 × 53.98 mm (3.37 × 2.13 in)
A4 paper: 210 × 297 mm (8.27 × 11.69 in)
US Letter paper: 8.5 × 11 in (215.9 × 279.4 mm)
US quarter: 24.26 mm (0.955 in) across
1 euro coin: 23.25 mm (0.915 in) across
AA battery: about 50.5 mm long and 14.5 mm wide