Screen Ruler
Measure pixel distances anywhere on your screen using an on-screen overlay with image edge detection. Pick a measuring mode — Bounds, Spacing, Horizontal, or Vertical — and Screen Ruler snaps to color edges under your cursor so you can size up UI elements without leaving your workflow.
Getting Started
Requirements
Screen Ruler needs Screen Recording permission so it can see the pixels under your cursor and snap to edges. If you haven't granted it yet, ProToys will let you know.
To grant it manually: open System Settings → Privacy & Security → Screen Recording and tick ProToys.
How to use
- Press ⌃⌘⇧M to bring up the ruler overlay.
- Pick a mode from the toolbar: Bounds, Spacing, Horizontal, or Vertical.
- Move the cursor over the element you want to measure — the overlay snaps to detected edges and shows the dimensions in pixels.
- Click to copy the current measurement to the clipboard.
- Press Esc or click ✕ on the toolbar to dismiss.
Scroll the mouse wheel while the overlay is active to fine-tune the pixel tolerance live — useful when an edge is being missed or when the ruler keeps snapping past it.
Measuring Modes
| Mode | Behavior |
|---|---|
| Bounds | Click and drag to draw a measurement rectangle. The label shows width × height in pixels. Hold Shift while dragging to lock to a square. |
| Spacing | The overlay snaps to both horizontal and vertical edges around the cursor and reports W × H of the detected region. |
| Horizontal | Measures only the horizontal span of the region under the cursor. |
| Vertical | Measures only the vertical span of the region under the cursor. |
Keyboard Shortcuts
| Action | Shortcut |
|---|---|
| Toggle the ruler overlay | ⌃⌘⇧M |
| Switch to Bounds mode | ⌃1 |
| Switch to Spacing mode | ⌃2 |
| Switch to Horizontal mode | ⌃3 |
| Switch to Vertical mode | ⌃4 |
| Lock to square (Bounds) | Hold Shift while dragging |
| Adjust pixel tolerance | Mouse wheel scroll |
| Copy measurement | Click anywhere on the overlay |
| Dismiss | Esc |
Settings
Open ProToys Settings → Screen Ruler to configure the ruler. All settings persist between sessions and apply live while the overlay is open.
| Setting | Description |
|---|---|
| Activation shortcut | The keyboard command that toggles the overlay on or off. Default: ⌃⌘⇧M. |
| Default mode | The measuring mode used when the ruler is activated — Bounds, Spacing, Horizontal, or Vertical. Default: Bounds. |
| Capture screen continuously during measuring | When off, Screen Ruler takes a single snapshot when you open it. When on, it keeps re-reading the screen as you move. Useful for animated content, but uses a bit more battery. |
| Per color channel edge detection | Stricter mode that compares each color channel separately. Turn this off for gentler matching that works better on gradients and soft shadows. |
| Edge sensitivity | How forgiving the edge detection is. Higher values are more relaxed with gradients, shadows, and soft edges. Default: 30. You can also tweak it live by scrolling the mouse wheel. |
| Extra units of measurement | Choose an alternate unit shown alongside pixels — None (pixels only), Inches, Centimeters, or Millimeters. |
| Draw feet on cross | Adds small, serif-like "feet" at the ends of each measurement line for additional visual recognition. |
| Line color | The color of the measurement line and bounding box. |