Online RulerHow to measure a key on screen
Lay the key flat against a calibrated AR Ruler screen and measure from the outer end of the head to the tip of the blade. Align the blade with the scale so the reading follows the key's length. If you need the blade length for a case or holder, start at the shoulder where the blade meets the head.
- The website and desktop or browser extension rulers offer centimeters or fractional inches.
- If the key head sits away from zero, move the marker to each end of the key and subtract the smaller reading from the larger.
- Card calibration stays on the device and uses the card's physical size. It reads no card data and uses no upload or sensors.
- Open AR Ruler on the screen you plan to use. Choose a unit and calibrate against a physical bank card. The nominal ISO ID-1 card measures 85.60 mm across its long edge and 53.98 mm across its short edge.
- Take the key off its ring if you can. Set it flat with the blade parallel to the scale. Place it gently and pick it up when you need to shift it.
- Line up the outer edge of the head with zero. Use the point farthest from the tip along the length of the key. Look straight down and move the marker to the blade tip.
- Lift the key, set it back down, and take another reading. If the readings differ, check that the blade is straight, the near edge lines up with zero, and the marker is at the far edge. Write down the reading and the unit.
Line up a rounded head
A round or offset head can make the start hard to judge. Picture a line across the head at a right angle to the blade. Move that line outward until it just touches the head. Line up that point with zero, even if the widest part of the head sits off to one side.
Read just the blade
Find the shoulder, the step where the narrow blade meets the wider part of the key. Start at that step and read to the tip along the blade. Some keys have a smooth transition. If you use the edge of the head as your start, write that down so you can repeat the same measurement later.
Check the screen scale
Check the ruler against the same physical card after changing browser zoom or moving the ruler to another display. If AR Ruler detects a relevant change, the stored calibration may be out of date. If the card and the screen marks disagree, calibrate again before setting the key down.
Should I count the key ring?
Leave the ring out when recording the key's length. If you are checking a pouch, measure the attached pieces in the position they will sit inside it.
What if the head covers zero?
Move the key beside the scale. Match the head edge to the zero line and keep the blade parallel to the ticks.
Can I read between two ticks?
Record an approximate reading if the tip falls between marks. Use only the detail you can judge from the scale.