Straight Ruler · 1 Free
An on-screen ruler for your Mac.
Press ⌃⌥M and a precision ruler lies on top of whatever you’re looking at. Drag it into place, rotate it, and read the length — in real device pixels, matching your screenshots exactly.
Free to download · Requires macOS 15 or later
What it measures
- The length of anything along its edge
- Widths and heights of images, buttons, text and windows
- Distances at any angle — rotate it freely, with magnetic 45° detents
- Where you are along it: hover for a live reading like “128 px · 30%”
How to measure with the on-screen ruler
Show the instruments
Press ⌃⌥M in any app. The ruler appears over your screen without taking you away from what you’re doing.
Lay it along what you want to measure
Drag the ruler so its top edge — the one with the ticks — lines up with the thing you’re measuring. Drag an end to pivot it; double-click it, or press A, to swing between horizontal and vertical.
Read and copy the length
The readout shows the length in pixels. Press ⌘C to copy it, for example “240 px”. Press Esc when you’re done.
Keyboard shortcuts
- 1
- Choose the ruler
- ←→↑↓
- Nudge by 1 px — with ⇧, by 10 px
- []
- Rotate by 1° — with ⇧, by 15°
- A
- Swing between horizontal and vertical
- ⌘C
- Copy the measurement
Free or Pro?
The straight ruler is free forever — pixel-exact, at a fixed 640 points, in the Crystal style, with Enhanced Precision. Measure My Pro, a one-time purchase, lets you resize it freely and adds points, centimetres and inches.
Enhanced Precision — edge snapping, gap detection and a real-pixel loupe — is free and optional. It needs Screen Recording permission; everything else works without it.
Questions and answers
Is there a ruler on the Mac screen?
macOS doesn’t include an on-screen ruler. Measure My adds one: press ⌃⌥M and a precision ruler lies over any app, ready to drag, rotate and read.
Is the screen ruler free?
Yes. The straight ruler is free forever, at a fixed length of 640 points, reading real pixels, with the Crystal style and Enhanced Precision. Measure My Pro lets you resize it freely and adds points, centimetres and inches.
Does it measure in pixels or points?
In real device pixels by default — the numbers your screenshots show. On a Retina display, a card 160 points wide reads 320 px. Measure My Pro adds points, centimetres and inches.
The other instruments
Corner Ruler
Pro An L-square that reads width and height from one corner at once. Learn moreCaliper
Pro Point-to-point distance, with ΔX and ΔY for diagonals. Learn moreRectangle Frame
Pro Width × height and aspect ratio of any rectangular area. Learn moreCircle Gauge
Pro Diameter and radius of round things — avatars, icons, buttons. Learn moreCrosshair
Pro Exact pixel coordinates anywhere, with an optional origin. Learn moreGap
Pro The spacing between two elements, horizontal or vertical. Learn moreAngle
Pro A protractor for angles between 0° and 180°. Learn moreGrid
Pro Column, baseline, square and dot grids across the whole screen. Learn morePixel Probe
Pro One pixel, magnified — with its exact coordinates. Learn more
Measure what you see.
A precision instrument for your screen — one shortcut away.