Ruler, Level & Protractor
Use your phone or monitor as a ruler (calibrated with a bank card), check level with the tilt sensor, and measure angles with an on-screen protractor. Measurements never go to a server.
The zoom level changed since calibration. Please calibrate again.
Hold a bank card (85.6 mm wide) against the dashed box and move the slider until the box is exactly as wide as the card. It only fits this screen.
Tap or drag on the ruler to see the length from the left end. Without calibration the browser's assumed size is used and may differ from reality.
Check level with your phone's tilt sensor. Lay it flat, or stand it up and rest the bottom edge on the object.
Sensors vary between devices. Use a real spirit level for precise work. Sensor values never go to a server.
Drag the red dot (or use arrow keys) to match the angle of an object on the screen. The center dot is the vertex.