Last updated: August 2026

About Accurate Ruler

Accurate Ruler is a free, browser-based measurement tool that turns any screen — desktop, laptop, tablet, or phone — into a precision ruler. Measure in centimeters, millimeters, inches, or pixels at actual physical size. No app to install, no account required, no ads.

Our Mission

Measurement should be instant, accurate, and free. We built Accurate Ruler because the alternatives were either inaccurate (defaulting to the outdated 96 PPI web standard), cluttered with ads, or missing basic tools like millimeter support and undo. We wanted something that felt like a professional instrument — not a throwaway utility.

What Makes Accurate Ruler Different

Millimeter support

Most online rulers offer only cm and inches. We add mm — essential for precision tasks like PCB layout, jewellery sizing, and small component measurement.

Four calibration methods

Auto-detect, device picker (400+ models), screen diagonal entry, or physical credit card alignment. Calibration is saved to localStorage — calibrate once, and every return visit is already accurate.

Undo / Redo for guide lines

Drop guide lines and make mistakes freely. Ctrl+Z undoes the last guide, Ctrl+Shift+Z redoes it. No other free online ruler offers this.

Rulers on all four edges

Activate Top, Bottom, Left, and Right rulers simultaneously for a full-frame measuring environment.

Crosshair mode

A live crosshair follows your cursor, showing real-time X and Y coordinates in your chosen unit — ideal for precise two-dimensional positioning.

Full keyboard control

1–4 for units, C for crosshair, D for theme, F for fullscreen, G for guide visibility, Esc to clear — every action has a shortcut.

Dark and light theme

Toggle with D or the toolbar button. Your theme preference is remembered between sessions.

Privacy First

Accurate Ruler runs entirely in your browser. We do not collect personal data, do not require an account, and do not track your measurements. Your calibration settings, theme preference, and unit choice are stored locally on your own device using localStorage — never transmitted to our servers. Read our Privacy Policy for full details.

Who Uses Accurate Ruler

→Graphic and web designers checking element sizes, margins, and spacing directly on screen
→Architects and engineers verifying scale drawings and blueprints
→Students and teachers measuring printed diagrams, maps, and worksheets
→Tailors and crafters measuring fabric, paper templates, and materials placed against the screen
→Photographers comparing filter thread sizes, sensor dimensions, and print proportions
→DIY enthusiasts getting quick measurements when a physical ruler is out of reach

Have a question or found a bug? Contact us →

Open the ruler