# Ruler

> A free online screen ruler in centimeters, millimeters and inches for phones, tablets and desktop browsers. Calibrate the screen with a physical reference before measuring actual size.

The interactive ruler measures small objects that fit within the visible screen area. It supports two movable endpoints, snapping, equal span divisions, unit conversion, Freeze, Copy and a fullscreen view. On mobile, the default direction follows the longest browser edge. Browsers without fullscreen support expand the ruler within the browser window.

Physical calibration uses a standard bank card, a supported coin or a marked ruler. Compatible iPhones can start from a display-specification estimate, with optional model selection. An estimate is not a verified calibration. Saved physical calibration takes priority; browser zoom, display scaling or changing screens can require a new check.

Reference matching requires a person to compare an actual object with the screen. A screenshot or a device estimate alone cannot verify physical accuracy. The tool is not a camera, AR ruler or long-distance tape measure.

The screen ruler runs locally in the browser without an account, camera or photo upload. Calibration and preferences are saved in that browser when local storage is available. Endpoints and Freeze are temporary. A precise fit should be checked with a suitable physical measuring tool.

The separate Distance to friends feature compares approximate straight-line distances between shared location snapshots. It uses a temporary online room for up to eight people, with no accounts. Anyone with the room link can view and join; it is not live location tracking. Shared rooms expire after ten days without an explicit visit or update. Room pages are not intended for search indexing.

Compare measurements puts two object lengths on one proportional scale and shows their difference. A label, optional names and measured values travel in a snapshot link. A reply creates a new link; earlier links do not update. There is no comparison server record, automatic expiry or revocation, and anyone with a link can read or edit its contents. Shared comparison pages are not intended for search indexing.

## Ruler and guides

- [Online ruler](https://ruler.shesek.co/): Open the measuring tool, calibrate the screen, choose units and place endpoints. Includes feature explanations, instructions and frequently asked questions.
- [Calibrate a screen ruler](https://ruler.shesek.co/guides/calibrate-screen-ruler/): Match a bank card, supported coin or physical ruler; understand iPhone estimates, zoom changes and accuracy limits.
- [Measure distance between friends](https://ruler.shesek.co/guides/distance-between-friends/): Understand shared location snapshots, straight-line distance, group ruler marks and the limits of city or device estimates.
- [Measure without a ruler](https://ruler.shesek.co/guides/measure-without-ruler/): Choose between a calibrated screen and everyday reference objects, follow two illustrated examples, and distinguish measurements from rough estimates.
- [Read centimeters, millimeters and inches](https://ruler.shesek.co/guides/read-cm-inch-ruler/): Read metric ticks and inch fractions using worked examples and instructional diagrams. Guide diagrams are not actual-size measuring references.
- [Distance to friends](https://ruler.shesek.co/friends/): Learn how a shared distance ruler works, how friends join, and what location snapshots and link access mean before starting a room.
- [Compare measurements with a friend](https://ruler.shesek.co/compare/): Create an invitation, add a second measurement in centimeters or inches, and share back a two-person comparison. The chart is proportional, not an actual-size ruler.