Screen Ruler
A free on-screen ruler. Measure small objects in centimetres, inches or pixels directly on your screen — auto-detects common devices, or calibrate exactly with a standard card. Nothing uploaded.
Works best on a laptop or desktop with a mouse. On a phone, calibrate with a card or pick your exact model for the most accurate reading — auto-detect is a best guess.
Keyboard: C crosshair · A angle · D dark mode · F fullscreen · H hide controls · 1-4 units · Esc clear/close
How to measure with your screen
Choose cm, inch or px at the top.
Tap Left, Right, Top or Bottom to place a ruler along that edge of your screen.
Hold the object against the ruler edge, or move your mouse over the area to read exact x/y coordinates.
Where a screen ruler helps
Quickly check the size of a small object — a ring, a screw, a cable — without hunting for a real ruler.
Compare a ring's inner width against the ruler to estimate its size before buying online.
Get a rough real-world sense of a product's size from a photo or listing.
Cross-check a measurement in cm, inches or pixels while designing or laying out a document.
Benefits
- Switches between cm, inch and px instantly.
- Auto-detects many common phones and laptops for an accurate starting point.
- Card calibration for a genuinely accurate reading on any screen, saved for next time.
- Free, works in your browser — nothing is uploaded or tracked.
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Frequently asked questions
How accurate is an on-screen ruler?
It depends entirely on knowing your screen's true pixel density (PPI). Browsers can't detect a screen's physical size directly, so this tool auto-detects common devices as a best guess, and also offers a quick calibration using a standard credit/debit card — which gives a genuinely accurate result on any screen, not just recognised ones.
Why do I need to calibrate?
Auto-detect only recognises a set of common phones, laptops and monitors. If your device isn't in that list, or you've zoomed the page, the ruler can be off. Calibrating with a card (a fixed, standard size) corrects this in a few seconds and is saved for next time.
What do I need to calibrate?
Any standard credit, debit or ID card works — they're all the same size worldwide (85.6mm wide). Hold it up to your screen and drag the slider until the on-screen bar matches the card exactly.
Does this work on mobile?
Yes — auto-detect recognises many common phones, and you can always calibrate with a card for an exact reading on any device.
Is my data uploaded anywhere?
No. Everything — detection, calibration and measuring — happens entirely in your browser. Nothing is sent to a server.
Can I measure in pixels?
Yes — switch the unit to px to see exact on-screen pixel measurements, useful for design and development work.
Can I pick my exact phone or laptop model?
Yes — open Calibrate and switch to the Device tab, which lists common phones, tablets and laptops with their known screen size, so you can pick yours directly instead of relying on auto-detect.
Does it have a fullscreen mode?
Yes — tap Fullscreen to use the entire screen as the ruler, with the browser's address bar and tabs hidden for maximum measuring space. Press Escape or tap Exit fullscreen to return.
What is the crosshair for?
Turning on Crosshair draws a horizontal and vertical guide line through your cursor, so you can line up a point against two edges at once — handy for centring an object or checking alignment.
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