rulerRECOMMENDED
Credit or debit card
Use the 53.98 mm short edge of a standard bank card. Hold it upright and match the line to its width. No photo or card details needed.
Use a bank cardFREE SCREEN RULER · NO DOWNLOAD
Online ruler in cm, mm & inches.
Measure small objects on your screen in centimeters, millimeters or inches. Calibrate with a card, coin or ruler first.
BETWEEN A & B
1.97 in
Drag A and B to the edges of your object. Use Full screen for more room.
An endpoint is outside the visible ruler.
Resume Live to reposition the endpoints.
Use a physical reference before measuring. Recheck after changing browser zoom or moving to another screen.
Screen & scale
Browser screen information helps size the ruler. A physical reference is still needed to calibrate it.
5 cm1.97 in
Ruler controls
Free to use No ads or tracking Calibration stays in your browser
FROM SCREEN TO REAL LIFE
How to use
an online ruler.
Measure a button, paper strip or small gap directly on your phone, tablet or computer screen. Check the scale, line up the edges, then read the distance.
- 01
Set your screen’s scale
Choose Calibrate screen. Choose a standard bank card, a supported coin or a marked length on a physical ruler. Match the guide to that reference. Save only after checking the physical match. Follow the calibration guide.
- 02
Line up the edges
Hold a small object beside the ruler and drag A and B to its edges. Choose Full screen for more room, or a vertical ruler for taller objects. The tick spacing stays at your calibrated scale.
- 03
Take the measurement with you
Read the distance in cm or inches. Freeze it to lock the endpoints, switch units, or copy both readings. Use equal parts for simple spacing projects, or compare a measurement with a friend.
A QUICK REFERENCE
Read centimeters,
millimeters & inches.
The metric ruler shows centimeters with millimeter ticks. The inch ruler has marks every 1/16 inch. With snapping on, endpoints settle on those marks.
Switching units preserves the exact positions you picked. Displayed values are rounded; copied values match the readout. See tick examples and inch fractions.
1 inch=2.54 cm
1 cm=10 mm
5 cm≈1.97 inches
Conversion is exact. Physical screen spacing depends on your calibration.
MEASURE WITH CONFIDENCE
Ruler guides.
Measure without a ruler
Have a phone, bank card or coin? Choose a method and follow two illustrated examples.
Find a measuring method →Calibrate your screen ruler
Use a card or coin when you have no physical ruler. Match the scale and learn when to check it again.
Read calibration guide →How to read a ruler
Follow illustrated cm and mm examples, read inch fractions and convert them to decimals.
Read ruler guide →Measure distance between friends
Compare shared snapshots, read the group ruler and understand straight-line distance.
Read distance guide →MEET THE IPHONE & IPAD APP
Keep a ruler
in your pocket.
Our companion app adds a magnified tick view for careful endpoint placement, independent nudging, and full-screen measuring. It also has equal divisions, Freeze, unit conversion, and Copy.
Built for iPhone and iPad. Works offline, without accounts, ads, or tracking.
View on the App StoreApp Store link coming when the app is available.
GOOD TO KNOW
Before you measure.
Is this online ruler actual size?
After you match it to a physical reference, its spacing follows your calibration. A browser cannot reliably know your display’s physical dimensions. Until calibrated, the ruler is a preview, and its markings may not match real centimeters or inches.
Can I calibrate an online ruler without a real ruler?
Yes. Choose a standard credit or debit card, or one of the supported coins, in Calibrate screen. Match the card’s short edge to the line or the coin’s outer edge to the circle. Confirm only after comparing the physical object. Business cards and unidentified coins are not reliable substitutes. See the card and coin calibration guide.
How can I measure an inch without a ruler?
Calibrate with a standard bank card or a supported coin, select in, and compare the interval from 0 to 1 with your object. A US quarter is slightly shorter than an inch, so use its exact calibration preset. Follow the one-inch measuring steps.
How do I use the online ruler on my phone?
Open this page in your browser, calibrate with a card or coin, and drag A and B with your finger. On touch screens, the ruler starts along the longer edge: vertical in portrait and horizontal in landscape. It follows rotation until you choose a direction with the arrow buttons. Full screen fills the display where supported, or expands within the browser window. No app download is required. The same ruler works on tablets and computers with a mouse or keyboard; check calibration on each screen.
What happens if I zoom or change monitors?
Recheck calibration after browser zoom, display scaling, or a screen change. We flag changes the browser exposes, but not every monitor change can be detected. A saved calibration is a convenience, not a guarantee that the current screen still matches.
Can I measure something longer than my screen?
The ruler uses the available width or height at your calibrated scale. Choose Full screen or rotate your device for more room. Full screen uses the whole display where supported; otherwise it fills the browser window. For objects that still do not fit, use a physical ruler or tape measure. Resizing never stretches the tick spacing to make an object fit.
How do equal divisions work?
Place the endpoints around a length, then choose a number of parts. For example, a 6 cm span divided into 3 parts gives three 2 cm sections. The guides show each boundary, useful for spacing marks on paper or planning small craft projects.
Where is my information saved?
Your screen-ruler calibration and unit preference stay in this browser’s local storage when available. Screen measurements are not sent to us. Optional measurement comparisons keep the label, names and lengths in the shared link; replies create a new link. The optional distance-to-friends experience stores the name and location snapshot you choose to share in a temporary room. Read how sharing and location work. There are no analytics, ads, third-party fonts, or accounts.