Online Millimeter Ruler (MM)
Actual size millimeter ruler calibrated to your screen. Fine 1mm graduation lines, 5mm mid-ticks, and 10mm numbered intervals for engineering and crafting.
Measurement Field
Place physical objects directly on screen, drag calipers, or tap rulers to drop guides.
Engineering & Hardware Sizing Guide
Millimeter measurements are the universal standard for mechanical engineering, CAD modeling, and 3D printing. Common metric hardware reference sizes:
- • M2 Screw Diameter: 2.0 mm
- • M3 Screw Diameter: 3.0 mm (standard 3D printer hardware)
- • M4 Screw Diameter: 4.0 mm
- • Standard Credit Card Thickness: 0.76 mm
- • MicroSD Card Width: 11.0 mm × 15.0 mm
Sub-Millimeter Screen Precision
Because high-DPI displays have hundreds of physical pixels per inch, modern web canvases can render tick graduation lines down to tenths of a millimeter. For highest accuracy when measuring small parts:
- Calibrate using a physical credit card with known 85.60 mm width.
- Use Crosshair Mode (Press C) for live coordinate tracking.
- Use fullscreen mode (Press F) to eliminate browser viewport borders.
Millimeter Ruler FAQ
Technical details on screen PPI, calibration accuracy, and physical scale.
How many pixels are in 1 millimeter on a computer display?
The number of pixels per millimeter depends entirely on your screen physical pixel density (PPI). At a standard 96 PPI, 1 mm is approximately 3.78 pixels. On a 141 PPI laptop screen, 1 mm is approximately 5.55 pixels. On a 254 PPI MacBook Retina display, 1 mm is approximately 10 pixels.
Is this MM ruler accurate enough for 3D printing and engineering components?
Yes, provided your screen is calibrated using our physical verification step. Once calibrated, the high-DPI canvas renders ticks with sub-pixel antialiasing, making it ideal for checking small fasteners (M3, M4, M5 screws), coin diameters, and small electronics boards.
How do I measure small hardware parts like bolts and screws?
Align the head or flat edge of the fastener against the left 0 mm boundary. Place a guide line on the ruler and drag it directly to the far tip of the fastener to read the exact length in millimeters.