Online Ruler (Actual Size)
No ruler at hand? Calibrate once with a card and your screen becomes a real-size ruler.
Drag along the ruler to measure a length.
Calibrate with a card (most accurate)
Hold a credit or bank card against the blue frame and make the frame exactly the same size as the card.
Calibrate with your screen size
If you know the diagonal size of your computer or tablet screen.
Your calibration is stored only in this browser on this device. Nothing is sent anywhere.
How to use
- 1. Calibrate with a cardHold a credit or bank card over the blue frame and adjust the slider or −/+ until the frame matches the card exactly, then click "Calibrate to this size".
- 2. Place the objectLine up one end of the object with the left edge (0) of the ruler.
- 3. Read or dragRead the marks, or drag along the ruler with your finger or mouse to see the length.
Card size (international standard)
- Credit cards, bank cards and many ID cards use the ISO/IEC 7810 ID-1 size
- 85.60 mm × 53.98 mm
Sources: ISO/IEC 7810:2003 Identification cards — Physical characteristics
FAQ
Who is this for?
Anyone who needs to measure something small right now without a ruler: a screw, a ring, a button, a sheet of paper or a small part. It is also handy to check the size of something you are buying online, or when all you have is your phone.
Is an on-screen ruler really accurate?
Before calibration, the ruler assumes the standard web size (1 inch = 96 pixels), which differs between devices. After you calibrate once with a card or your screen size, it matches your device much more closely. "Calibrated" at the top means it has been set.
Why calibrate with a card?
Credit cards, bank cards and many ID cards follow the international standard ISO/IEC 7810 ID-1: 85.60 mm × 53.98 mm. Almost everyone has one, and they are all the same size, so they make a good reference.
How do I calibrate with a card?
Place the card on the blue frame and move the slider, or press − and +, until the frame is exactly the size of the card. Then click "Calibrate to this size". Lining up a corner of the card with a corner of the frame makes it easier.
The card does not fit on my phone
On narrow screens such as phones, the frame turns upright. Hold the card upright too.
How do I calibrate with my screen size?
Enter the diagonal size of your screen in inches and click "Calibrate to this size". You can find it in your device's specifications. Display scaling settings can throw this off, so calibrating with a card is more reliable.
Does it stay calibrated?
Yes. Your calibration is saved in this browser on this device, so it is ready next time. On another device or browser, calibrate again. "Reset" returns to the starting state.
How do I measure by dragging?
Drag along the ruler for the length you want to measure. Red lines mark the start and end, and the length appears below. A single tap shows the reading at that point.
Can I switch between cm and inches?
Yes, with the "cm" and "inch" buttons at the top. Centimetres are marked every millimetre, inches every 1/16 inch.
Can I measure things longer than the screen?
Only up to the width of the screen. Measure longer things in parts, or use the full-screen button to make the ruler as long as possible.
What if I zoom the page?
Changing the browser zoom after calibrating shifts the marks. If you change it, calibrate again.
Is anything sent anywhere?
No. Your calibration is stored only in this browser on this device.
What can't it do?
It is not suited to very fine measurements (0.1 mm precision) or to work where exact dimensions matter. Use it as a guide and check important measurements with a real ruler or calipers.
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