Measure objects at actual size directly on your screen. Calibrate with a credit card for best accuracy.
An online ruler is handy when you don't have a physical ruler nearby. It's perfect for quick measurements of small objects like phone dimensions, jewelry sizing, craft supplies, or checking the size of items for online purchases. Since it runs entirely in your browser, there's nothing to download or install.
The ruler supports both centimeters and inches, making it useful regardless of which measurement system you prefer. The PPI adjustment ensures accuracy across any screen type — from laptops to desktops to tablets.
| Device Type | Typical PPI | Examples |
|---|---|---|
| Standard Desktop | 96 PPI | Most 24" and 27" monitors at 1080p |
| Laptop | 110–150 PPI | MacBook Air (227 PPI), ThinkPad (141 PPI) |
| 4K Monitor | 140–163 PPI | Dell 27" 4K (163 PPI), LG 27" 4K (163 PPI) |
| Retina Display | 220–264 PPI | MacBook Pro 14" (254 PPI), iPad Pro (264 PPI) |
| Smartphone | 300–500 PPI | iPhone 15 (460 PPI), Galaxy S24 (416 PPI) |
| Card Type | Width | Height |
|---|---|---|
| Credit/Debit Card (ISO/IEC 7810 ID-1) | 8.56 cm (3.37 in) | 5.398 cm (2.125 in) |
| Standard Business Card | 8.9 cm (3.5 in) | 5.1 cm (2.0 in) |
Accuracy depends on your screen's pixel density (PPI). For best results, calibrate the ruler by placing a credit card (8.56 cm wide) against the screen and adjusting the PPI slider until the ruler matches. After calibration, accuracy is typically within 1-2mm.
Different screens have different pixel densities (PPI). A 1080p 24-inch monitor has about 92 PPI, while a phone might have 400+ PPI. The ruler auto-detects your screen PPI, but calibration with a known object gives the best accuracy.
Yes, but phone screens have high pixel density and the ruler may appear small. Calibrate with a credit card or bank card for accurate results. Hold the phone in landscape mode for a longer ruler.
Place a standard credit card (8.56 cm / 3.37 inches wide) flat against your screen. Adjust the PPI slider until the ruler's 8.56 cm mark aligns exactly with the card's edge. Your ruler is now calibrated for your screen.
PPI stands for Pixels Per Inch. It tells you how many pixels fit in one inch of your screen. A standard desktop monitor is about 96 PPI, while a Retina display is 192+ PPI. The ruler needs to know your PPI to display accurate real-world measurements.
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