A4 Ruler — 210 mm Actual Size
A ruler spanning exactly 210 mm — the width of an A4 sheet of paper. Calibrate to your screen and lay an A4 sheet against it to verify your calibration.
Place a physical credit card on your screen. Drag the slider until the dashed box matches the card exactly, then click Apply.
About This A4 Ruler
This ruler spans exactly 210 mm — the width of an A4 sheet of paper as defined by ISO 216. It's useful for verifying print output, checking that a PDF exported at A4 size prints correctly, and measuring paper-related dimensions.
A4 is the most widely used paper format in the world outside North America. For US Letter (215.9 × 279.4 mm), see the US Letter size guide. For A3 (297 × 420 mm), see the A3 paper size guide.
Frequently Asked Questions
What is A4 paper size?
A4 paper is 210 × 297 mm (8.27 × 11.69 inches). This ruler shows the 210 mm width of an A4 sheet — so you can verify that a sheet of A4 paper laid on your screen matches the ruler exactly after calibration.
Is this A4 ruler actual size?
Yes — after calibration. Click "Calibrate" and use a physical credit card to set your exact screen PPI. Once calibrated, the ruler spans precisely 210 mm — matching the width of a real A4 sheet.
How does 210 mm compare to inches?
210 mm = 21 cm = 8.268 inches. The inch scale on the bottom edge of this ruler shows the equivalent measurement. A4 width (210 mm) is approximately 8 and a quarter inches.
How wide is A4 paper in cm?
A4 paper is exactly 21.0 cm wide and 29.7 cm tall. In inches: 8.27 × 11.69 inches. The ISO 216 standard defines A4 as 210 × 297 mm.
What is the difference between A4 and Letter paper?
A4 is 210 × 297 mm (8.27 × 11.69 in). US Letter is 215.9 × 279.4 mm (8.5 × 11 in). Letter is slightly wider but shorter than A4. A4 is the international standard; Letter is used mainly in the US and Canada.
Can I use this ruler to verify my printer output?
Yes. Print a document at 100% scale (no scaling), then lay the printed sheet against your calibrated screen. The A4 ruler will confirm whether the 210 mm width printed correctly. If not, check your printer's paper size setting.