A 15 cm pocket ruler on your screen
A 15 cm ruler, about 6 inches, is the classic pencil-case size. It is also roughly the length of a modern phone screen, which makes it the most practical ruler to carry in your pocket. This page opens a centimeter ruler along the left edge of your screen, marked every millimeter.
Related guides: How to Measure Without a Ruler
How to use it
- Tap Calibrate and match a bank card, or let the ruler detect your phone.
- Hold the object against the left edge of the screen with one end at 0.
- Read the length in cm and mm. Switch to inches if you need them.
Good to know
- 15 cm = 150 mm ≈ 5.9 inches.
- A phone with a 6.1-inch screen shows about 14 cm along its long edge; a 6.7-inch phone about 15.5 cm.
- On a computer, the side ruler easily shows the full 15 cm.
Will 15 cm fit on your phone?
15 cm is 5.91 inches, just under 6 inches. Phone screens are sold by their diagonal size; the long side of a typical modern phone screen is:
| Screen (diagonal) | Long side | Fits 15 cm? |
|---|---|---|
| 5.4″ | 12.5 cm (4.9 in) | No |
| 6.1″ | 14.1 cm (5.5 in) | No |
| 6.3″ | 14.5 cm (5.7 in) | No |
| 6.5″ | 15.0 cm (5.9 in) | Almost |
| 6.7″ | 15.5 cm (6.1 in) | Yes |
| 6.9″ | 15.9 cm (6.3 in) | Yes |
- Figures are for the tall 19.5:9 shape most phones use today.
- The browser bars take some of the screen, so turn on fullscreen for the most length.
- On a smaller phone, measure in two steps: mark where the ruler ends, slide the object and add the lengths. Tablets and laptops fit 15 cm easily.
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