How to measure pixels on your Mac screen

What macOS can do

Apple's screenshot guide for macOS 26 covers capturing the entire screen, a window or a portion of it, and says nothing about measuring. Preview can show the size of a selection in an image:

1. Take a screenshot of what you want to measure, for example with Shift-Command-3 for the entire screen.
2. Open the screenshot in Preview.
3. If the Markup toolbar isn't showing, click the Show Markup Toolbar button, then click the Rectangular Selection button.
4. Choose Tools → Show Inspector, click the Crop Inspector button and choose a unit of measurement.
5. Drag over the part you want to measure. The Crop Inspector shows the dimensions of your selection.

The selection goes where you drag it, so its edges are only as exact as your hand, and you measure a picture of the screen rather than the screen. For the color of a pixel, Digital Color Meter shows the values of the color under the pointer.

Measure in Shotbolt

Measure Pro (Shotbolt Pro) finds edges in the pixels on screen, so the lines stop where a button, a picture or a column ends. Every download from this site starts with 7 days of Pro.

1. Click the Shotbolt icon in the menu bar and choose Tools → Measure Pro (Shotbolt Pro). The default shortcuts leave it without a key; you can add one in Settings → Shortcuts, under Tools.
2. The screen holds still and a hint bar shows the keys. Point at anything: lines run from the pointer to the nearest edges, with a label for the width and height between them. Hold Shift to see the four distances from the pointer.
3. For an exact spot, press the arrow keys to move the pointer one pixel at a time, or Shift and an arrow key for ten.
4. Click to pin a measurement, so it stays while you measure the next thing.
5. Press ⌘C to copy the size as text, such as 128 × 44 pt. Press Return to turn the display under the pointer into a screenshot with every measurement drawn in. It arrives like any other capture.
6. Press Esc, right-click, or press your Measure shortcut again to stop.

Measure needs the Screen & System Audio Recording permission, like every capture. Help and Features list every key.

Boxes, spacing and guides

• Boxes. Drag a rough box around a button or an image. When you let go, it shrinks to fit what is inside it. Hold ⌘ as you let go to keep the box as you drew it.
• Spacing. Click a box to select it, Shift-click a second one, then hold Option (⌥) to see the gaps between them. When one box sits inside the other, you see the distance from each of its edges to the outer box.
• Guides. Press H or V to add a horizontal or vertical guide at the pointer, labeled with its position. Measurements stop at a guide, so you can measure from an element to a line you set.
• Remove. Delete (⌫) removes the selected boxes or the newest measurement. ⌘⌫ removes them all.

Points or pixels

Measure starts in points. Press U to switch to pixels, and again to go back; the hint bar shows which one is on, and Shotbolt remembers it next time. A size in points is the size in pixels divided by the display's scale, so the two numbers match only on a display with a scale of 1. ⌘C copies the size in the unit on screen.

Colors and contrast

Press I, or hold Control, to inspect colors. The color under the pointer shows as HEX, RGB and HSL, and 1, 2 or 3 copies one of them. Click two colors, such as text and its background, to see their contrast ratio with a pass or fail for the WCAG 2.2 AA and AAA levels, for normal and large text. The ratio is never rounded up onto a pass. Help has more.

Limits

• Edges come from color. A line stops where a pixel differs enough from the one under the pointer. Soft shadows, gradients and smoothed text can stop a line early or let it run on. Press [ or ] to change the tolerance, which the hint bar shows as a percentage.
• A still picture. Measure reads the screen as it was when you started. Anything that changes after that, such as a video or an animation, stays as it was until you start again.
• One display at a time. A box stays on the display where you started it, and Return saves only the display under the pointer. Connecting or rearranging displays ends Measure.
• Clicks go to Measure. While it is on, clicking pins and selects instead of reaching the app below. Stop Measure to use the app.

Questions

Does it work in any app?

Yes. Measure reads the pixels on screen, so it works the same on a web page, a design file, a video frame or a picture, whatever app shows it.

Can I measure a menu or a hover state?

Yes. Open the menu or move the pointer over the element first, then start Measure with its keyboard shortcut. A menu that is open when you press it stays in the picture Measure reads.

More guides

• How to compare two screenshots on a Mac
• How to annotate an image on a Mac
• All guides