How to Use This Full-Screen Online Ruler

InchRuler.com provides the largest, most accurate online ruler. Simply select your device from the dropdown above for instant calibration, or use the ⚙️ button for advanced calibration with a credit card.

Quick Start

1. Select your device model from the dropdown (e.g., "MacBook Air 13.3")
2. Place your object against the screen
3. Drag the red line to measure, or click anywhere on the ruler
4. Toggle IN/CM to switch between inches and centimeters

Why This Ruler is Different

• Full-Screen Design: Maximizes measurement area - the ruler takes up your entire screen
• Instant Calibration: Just select your device model from the dropdown
• Auto-Detection: We automatically detect MacBooks, iPhones, and common displays
• Accurate to ±0.5mm: After calibration using a credit card reference
• Works Offline: Install as a PWA for offline access

Advanced Calibration

For maximum accuracy, click the ⚙️ button and use the credit card method:

1. Click the ⚙️ Calibrate button in the header
2. Choose "Credit Card" tab
3. Place a standard credit card (3.370" wide) on your screen
4. Adjust the slider until the blue rectangle matches your card exactly
5. Click Save - your calibration is stored permanently

MacBook Users

MacBook Air and Pro users: Select your exact model from the dropdown for automatic PPI calibration:

• MacBook Air 13.3" (M1/M2): 227 PPI (2560×1600)
• MacBook Air 13.6" (M2): 224 PPI (2560×1664)
• MacBook Pro 14": 254 PPI (3024×1964)
• MacBook Pro 16": 254 PPI (3456×2234)

Common Conversions

• 1 inch = 2.54 cm
• 3 inches = 7.62 cm
• 6 inches = 15.24 cm
• 12 inches = 30.48 cm (1 foot)