Millimeter Ruler (mm)
Every single millimeter is marked on this ruler, making it ideal for measuring small objects like screws, jewelry, or paper thickness.
Display settings
Calibration details
Resulting density: 96.0 PPI · Not calibrated · estimate only
Verify against a physical reference. Different displays can report identical parameters; display changes cannot always be detected.
Press and drag across the ruler to measure a distance in cm and inches.
Keyboard: focus the ruler and press Enter to start at zero, then Tab to − or + to adjust.
Measuring small objects in millimeters
Why calibration matters more at this scale
Before calibration, this ruler uses an initial estimate: the 96 CSS-pixel reference on fine-pointer desktops and a device-based estimate on touch screens. Neither knows your display's physical size. Match the outline to a bank card, then verify with a physical reference before relying on millimeter measurements; the methodology page shows the arithmetic.
Limits of a screen at millimeter level
Ticks cannot be finer than a CSS pixel, cover glass adds a small parallax offset, and the calibration slider moves in 0.5 CSS px steps. Pixel spacing, displayed decimals and measurement accuracy are different things; verify your setup with a physical reference. For tighter tolerances use calipers.
Millimeters to fractional inches
Imperial hardware is specified in fractions. The table gives the decimal inch value and the nearest 1/16 mark for common millimeter sizes.
| mm | Inches (decimal) | Nearest 1/16 in |
|---|---|---|
| 1 | 0.039 | 1/16 in |
| 2 | 0.079 | 1/16 in |
| 3 | 0.118 | 1/8 in |
| 5 | 0.197 | 3/16 in |
| 6.35 | 0.250 | 1/4 in |
| 10 | 0.394 | 3/8 in |
| 12.7 | 0.500 | 1/2 in |
| 15 | 0.591 | 9/16 in |
| 20 | 0.787 | 13/16 in |
| 25.4 | 1.000 | 1 in |
Related tools
For parts you cannot lay on the screen, photograph them beside a ruler or a bank card and use the image measurement tool. For any value use the unit converter; for imperial hardware switch to the inch ruler.
How to use this ruler
- Calibrate with a bank card before measuring small parts; a 3% error is a whole millimeter on a 30 mm object.
- Keep the mm tab selected: labels count in tens of millimeters and every short mark is 1 mm.
- Lay the object flat against the screen at the 0 mark and look straight down at its far edge to avoid parallax.
- Drag along the ruler to see a one-decimal-mm readout; the displayed decimal is not an accuracy guarantee.