Paper Size Reference & Converter
The ISO 216 standard defines the A and B series paper sizes used worldwide. Each A-series sheet is exactly half the area of the previous size — A0 (841 × 1189 mm) down to A8 (52 × 74 mm) — all sharing the same √2 aspect ratio so that folding any sheet in half produces the next size with no wasted paper. The B series fills the gaps between A sizes and is commonly used for posters, books, and envelopes.
US paper sizes such as Letter (8.5 × 11 in), Legal (8.5 × 14 in), and Tabloid (11 × 17 in) follow a different, non-proportional convention rooted in historical printing practices. This tool lets you select any standard format and instantly see its dimensions in millimetres, centimetres, inches, and pixels at your chosen DPI — essential for print design, web graphics, and document layout work.
How it works
ISO A-series: width_n = 1000 × 2^(−1/4 − n/2) mm, rounded to nearest mm. Pixels = (dimension_mm / 25.4) × DPI. 1 inch = 25.4 mm exactly.
Use cases
- Configuring correct canvas size for a print-ready PDF or illustration
- Calculating pixel dimensions for a document scan at a given resolution
- Comparing ISO and US paper formats when ordering international print runs
- Setting up poster or banner designs in the correct physical dimensions
- Verifying envelope and insert size compatibility for direct-mail campaigns
Frequently asked questions
What are the dimensions of A4 paper?
A4 measures 210 × 297 mm (21 × 29.7 cm), which is approximately 8.27 × 11.69 inches. It is exactly half of an A3 sheet and double an A5 sheet, and like all ISO 216 A-series sizes it keeps the √2 aspect ratio. At 300 DPI an A4 page corresponds to 2480 × 3508 pixels.
What is the difference between A4 and US Letter?
US Letter measures 8.5 × 11 inches (215.9 × 279.4 mm), so it is about 6 mm wider and 18 mm shorter than A4 (210 × 297 mm). A4 follows the ISO 216 standard with its proportional √2 ratio, while Letter comes from a historical US convention with no fixed aspect ratio across sizes. Documents designed for one format often need margin adjustments to print correctly on the other.
How many pixels is an A4 page at 300 DPI?
Using pixels = (dimension in mm ÷ 25.4) × DPI, an A4 page (210 × 297 mm) is 2480 × 3508 pixels at 300 DPI, the standard resolution for print. At 72 DPI the same page is 595 × 842 pixels, and at 150 DPI it is 1240 × 1754 pixels. This tool computes the pixel dimensions for any DPI you enter.
Why do A-series paper sizes use the √2 aspect ratio?
The √2 ratio (about 1:1.414) is the only aspect ratio that stays identical when a sheet is folded or cut in half across its longer side. That means every A size scales to the next one with no wasted paper — A0 (841 × 1189 mm, one square metre in area) halves into A1, A1 into A2, and so on down to A8 (52 × 74 mm).
What are B-series paper sizes used for?
ISO B sizes fall between consecutive A sizes — each B dimension is the geometric mean of the two neighbouring A sizes. They are commonly used for posters (B1, B2), books (B5), envelopes, and passports (B7), where an intermediate format works better than the A series. Like the A series, all B sizes share the √2 aspect ratio.