Image Ruler
Measure objects inside an image using a known reference object.
Select a photo containing the target object and a known reference (credit card, coin, or ruler).
3-Step Guide to Measuring Photos Accurately
Place a standard reference object (e.g. credit card or coin) flat beside the item you want to measure and shoot directly from above.
Upload your photo and drag the gold reference markers to cover the known object. Enter its exact size (default 85.60 mm).
Switch to Measure mode and drag the orange calipers across any object feature to read its true dimensions in mm, cm, or inches.
Prefer measuring directly against your monitor or phone glass? Check out our Online Ruler, calibrate your display with the Screen Calibration Wizard, or try our Digital Caliper.
Frequently Asked Questions About Image Measurement
Common questions about photo scaling, client-side security, and reference objects.
How does the online image ruler work?▼
The image ruler calculates real-world dimensions using proportional scaling against a known reference object in your photograph. By aligning two reference endpoints across an object of known size (such as a standard 85.60 mm credit card or coin), ANRuler establishes the exact pixels-per-unit scale for that image plane.
Is my photo uploaded to your server?▼
No. All image processing, rendering, and measurement calculations happen strictly within your local browser's memory using HTML5 Canvas and native URL objects. Your photo is never transmitted over the internet or stored on our servers.
What reference objects work best?▼
Any object with standardized dimensions works well: an ISO/IEC 7810 credit card (85.60 mm wide), a US quarter coin (24.26 mm), a 1 Euro coin (23.25 mm), or a physical millimeter ruler placed adjacent to your target subject.
What affects the accuracy of image measurements?▼
Image measurement depends on camera perspective, lens distortion, and coplanarity. For maximum accuracy, photograph your object and reference flat from directly above (90° perpendicular), minimize optical zoom distortion, and ensure both objects rest on the exact same plane.