Put your photo in perspective.
Add a photo, mark an object of known length, then measure another distance in the same plane.
A place for a little precision.
Align your object with the ruler.Drag the handles to mark both ends.
Measure twice.
Make once.
Set your scale
Use a known length in your image as a reference.
Find your edges
Drag the points to the ends of your object. Use arrow keys for careful adjustments.
Keep the details
Switch units, save a measurement, or export your list for the project ahead.
How to measure an object in a photo
Add an image and place A and B at the ends of a known length. Enter that length in millimeters and choose Set reference from points. Move A and B to another object to measure it. Reference and target must lie in the same plane: an angled photo can distort sizes. Screen calibration is independent of photo calibration.
A few small answers.
Better measurements start with knowing your tools.
Is this ruler actual size?
Only after you calibrate it to your screen. The initial scale is an estimate. Match a known physical length using Calibrate screen, then check against another object.
Can I measure an object in a photo?
Yes. Use Photo ruler, upload an image and mark a known reference length. Then mark the distance you want. Both objects must be in the same plane; perspective and lens distortion can affect the result.
Does my image leave my device?
This tool processes the selected image locally in your browser. No image upload service or third-party analytics is included.
What if I change my zoom or monitor?
Calibrate again. We flag detectable screen setting changes, but cannot reliably identify every external display. Check the ruler against a known object whenever your setup changes.
Can I use inches and fractions?
Yes. The inch ruler has sixteenth-inch ticks. Its secondary readout shows a fraction rounded to the nearest sixteenth, alongside metric conversions.