Measure anything on your screen—accurately
sruler.com is a fast, precise on-screen ruler. Set your screen scale one time using a known object (like a credit card or coin) and you can measure photos, UI elements, product images, documents, craft patterns—anything visible on your display. The ruler shows inches, millimeters, and a tape-style fraction for quick real-world matches.
Quick start
- Click Recalibrate.
- Place a credit card (85.60 mm), US quarter (24.26 mm) or any known width between the red lines.
- Drag until the lines match your object, then click Calibrate → Done.
- Drag the blue handle on the ruler to measure. Press R anytime to recalibrate.
Calibration stores the pixels-per-millimeter value for this device so measurements track reality—not guesses.
Why calibration matters
Every display is different. Browser zoom, operating-system scaling, and even sub-pixel rendering can shift how many pixels represent one millimeter. Instead of assuming your monitor’s size, sruler.com derives the true scale from your device. If zoom changes significantly, we’ll prompt you to recalibrate to keep results tight.
What people use this for
- E-commerce & marketplace sellers: verify photo sizing, compare dimensions in product shots.
- Design & UI work: sanity-check spacing, icon sizes, line lengths across screenshots.
- Makers & crafts: match printable patterns, beads, stitching, or cut lengths without a physical ruler.
- Hardware checks: measure screws/bolts on a laptop, envelopes, labels, or small parts in a pinch.
- Education: quick classroom demos of inches vs. millimeters and fractions.
Accuracy tips
- Use a rigid reference (credit card works perfectly). Avoid flexible objects.
- Zoom should stay consistent. If you change it, recalibrate.
- For tiny measurements, enable Snap to round to neat fractions.
- Ambient glare can create parallax—look straight at the screen when aligning.
Accessibility & keyboard
The interface supports pointer and keyboard usage. Key shortcuts: R (recalibrate), Esc (close), and the handle responds to standard pointer events on touch screens. Colors meet contrast expectations on dark backgrounds.
Coming soon
- PPI & aspect calculators and a few quick utilities that pair well with the ruler.
FAQ
Is this accurate on phones and tablets?
Yes—after calibration. The tool measures using your device’s exact pixel density and zoom. If you rotate the device or switch zoom, recalibrate for best results.
Can I measure in both inches and millimeters?
Yes. The readout shows decimal inches, a tape-style fraction to 1/16", and millimeters simultaneously.
Do you store my measurements?
No. Calibration is saved locally in your browser (localStorage) and never sent to a server.
Why does the page sometimes ask me to recalibrate?
If your browser zoom/dpr changes enough to affect precision, sruler.com asks you to re-confirm scale so you keep accurate measurements.