A little more precision.
Your everyday measuring desk. Calibrate your screen, line up an object, and let the little details add up.
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
Match a card or a known length to your screen. Your calibration stays in this browser.
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.
Online ruler in cm, mm and inches
Measure small, flat objects with a ruler calibrated to your display. Metric marks show millimeters within centimeters; inch marks show sixteenths. Use horizontal or vertical mode, or switch to CSS pixels for on-screen layout checks. Start at the zero tick rather than the edge of your display.
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.