Paper Size Converter
Look up the exact dimensions of any ISO A, B or C series paper size or North American size (Letter, Legal, Tabloid, ANSI) in millimetres, centimetres or inches, together with area and aspect ratio.
Look Up Any Paper Size in mm and Inches
Paper Sizes Formula
Where:
- \(w\) — width of the sheet in portrait orientation (mm)
- \(h\) — height of the sheet in portrait orientation (mm)
- \(A_n\) — area of size A\(n\) (m²)
- \(n\) — number of the size in the A series (A0 has \(n = 0\))
- \(d_{\mathrm{mm}}\), \(d_{\mathrm{in}}\) — the same length in millimetres and inches; 1 inch is exactly 25.4 mm
The ISO A series is defined by two rules: every sheet has an aspect ratio of \(1 : \sqrt{2}\), and A0 has an area of exactly 1 m². Each smaller size is the previous one folded in half, which halves the area. B and C series sizes are derived from the A series: B\(n\) is the geometric mean of A\(n\) and A\((n+1)\), and C\(n\) is the geometric mean of A\(n\) and B\(n\) — which is why C envelopes fit A sheets.
Paper Sizes – Calculation Example
Example: you leave the default selection — paper size A4, dimensions in millimetres.
\[ w = 210\ \mathrm{mm}, \qquad h = 297\ \mathrm{mm} \]
\[ A = 210 \times 297 = 62\,370\ \mathrm{mm^2} = \frac{62\,370}{645.16} \approx 96.67\ \mathrm{in^2} \]
Result: A4 measures 210 × 297 mm (8.27 × 11.69 in), has an area of 62,370 mm² (96.67 in²) and an aspect ratio of 1 : 1.414 — the \(\sqrt{2}\) ratio shared by all ISO sizes.
How to use the calculator
- Open the Paper size dropdown and pick a size: ISO A0–A10, B0–B6, C-series and DL envelopes, or a North American size such as US Letter, Legal, Tabloid or ANSI C/D/E.
- Choose Show dimensions in — millimetres, centimetres or inches. The other two equivalents are always shown as well.
- Read the results: Width (short edge, portrait), Height (long edge, portrait), Area in mm² and in², and the Aspect ratio.
- Check the summary below the results: it names the series the size belongs to, its typical use, and a comparison table of the most common sizes (A2–A5, Letter, Legal, Tabloid) with your selected size highlighted.
What are paper size standards?
The ISO 216 standard, used almost everywhere outside North America, is built on a single idea: a sheet whose sides are in the ratio \(1 : \sqrt{2}\) keeps that same ratio when cut or folded in half. Starting from A0 (841 × 1189 mm, exactly 1 m²), each step down the series halves the area, so A4 is half of A3, A5 is half of A4, and so on. This makes scaling documents between sizes trivial — enlarge A4 by 141% and it fills an A3 sheet exactly.
The B series fills the gaps between A sizes (B5 sits between A4 and A5) and is common for posters, books and passports. The C series is reserved for envelopes: a C4 envelope takes an unfolded A4 sheet, a C5 takes A4 folded once, and the popular DL business envelope takes A4 folded in thirds. Envelopes and contents therefore match by design, without guesswork.
North American sizes follow a different logic: simple inch-based dimensions inherited from historical hand-made paper. US Letter (8.5 × 11 in) is the everyday office size, Legal (8.5 × 14 in) is for contracts and court documents, and Tabloid (11 × 17 in, also called ANSI B) doubles Letter. The ANSI series extends this pattern for engineering drawings up to ANSI E (34 × 44 in). Because Letter is about 6 mm wider but 18 mm shorter than A4, the two are not interchangeable — printing an A4 document on Letter or vice versa shrinks or crops the content slightly.
The aspect ratio in the results tells you the shape of the sheet: all ISO sizes show 1 : 1.414 (\(\sqrt{2}\)), while North American sizes use other ratios — Letter is 1 : 1.294, so it is proportionally wider. If you need to work with ratios in other contexts, the aspect ratio calculator does the same job for any two dimensions.
Reference table: ISO A series
| Size | Portrait (mm) | Portrait (inches) | Area |
|---|---|---|---|
| A0 | 841 × 1189 | 33.11 × 46.81 | 1 m² |
| A1 | 594 × 841 | 23.39 × 33.11 | 0.5 m² |
| A2 | 420 × 594 | 16.54 × 23.39 | 0.25 m² |
| A3 | 297 × 420 | 11.69 × 16.54 | 0.125 m² |
| A4 | 210 × 297 | 8.27 × 11.69 | 62,370 mm² |
| A5 | 148 × 210 | 5.83 × 8.27 | 31,080 mm² |
| A6 | 105 × 148 | 4.13 × 5.83 | 15,540 mm² |
Assumptions, limitations and tips
- All dimensions are portrait values: width is the short edge, height the long edge. For landscape, simply swap them.
- ISO dimensions are the exact millimetre values from ISO 216; inch values are rounded to two decimals. Real sheets may differ by a few tenths of a millimetre within cutting tolerances, and photo papers sold as “A4” or “Letter” sometimes have small manufacturer-specific trims.
- Printers and copiers usually list both A4 and Letter; using the wrong one causes scaling of about 94–106% or cropped margins. Check the paper tray setting in your region before printing.
- The areas are nominal sheet areas, not printable areas — margins, bleed and printer hardware limits reduce the usable surface.
- If you design for screens rather than paper, the CSS unit converter converts between px, pt, mm and other units used in web layouts.
- For scaling drawings and maps from one sheet size to another, the map scale calculator can help you work out real-world distances.
Frequently Asked Questions
How do I calculate the dimensions of an A-series paper size by hand?
Every A-series sheet has an area of \( \frac{1}{2^n} \) m², where \( n \) is the number in the name (A4 has \( n = 4 \), so 1/16 m²). Solve \( w \times h = A \) with \( h = w\sqrt{2} \), giving \( w = \sqrt{A/\sqrt{2}} \) and \( h = \sqrt{A\sqrt{2}} \). For A4 this yields about 210 mm × 297 mm. A quicker shortcut: divide the previous size's long edge by two and swap the edges.
Is A4 the same as US Letter?
No, and mixing them up is the most common printing mistake. A4 is 210 × 297 mm (8.27 × 11.69 in); US Letter is 216 × 279 mm (8.5 × 11 in). Letter is roughly 6 mm wider but 18 mm shorter. Printing an A4 document on Letter (or the reverse) forces the printer to scale the content by about 94–106% or to crop the margins, so always check which size the document and the paper tray are set to.
How do I convert paper dimensions between millimetres and inches?
Divide millimetres by 25.4 to get inches, or multiply inches by 25.4 to get millimetres — the inch is defined as exactly 25.4 mm, so this conversion is exact. For example, 210 mm ÷ 25.4 ≈ 8.27 in. For areas, divide mm² by 645.16 to get square inches, since one square inch equals 25.4² mm².
What is the smallest and largest standard paper size?
The ISO A series runs from A0 (841 × 1189 mm) down to A10 (26 × 37 mm, about the size of a postage stamp). In the North American ANSI series, the range is Letter/ANSI A (8.5 × 11 in) up to ANSI E (34 × 44 in). This calculator covers A0–A10, B0–B6, C-series and DL envelopes, and Letter through ANSI E.
Which envelope fits which paper size?
The ISO C series is designed so each envelope takes a specific A sheet: C4 fits an unfolded A4, C5 fits A4 folded once (or an unfolded A5), C6 fits A4 folded twice, and C3 fits an unfolded A3. The DL business envelope takes A4 folded in thirds. Because C sizes are the geometric mean of A and B sizes, the sheet always slides in with a small margin — no measuring needed.
What is the difference between A, B and C paper series?
The A series is the everyday standard (documents, letters, printers). The B series fills the gaps between A sizes — B5, for instance, sits between A4 and A5 — and is common for posters, books and passports. The C series exists purely for envelopes sized to hold A sheets. All three share the 1 : √2 aspect ratio, so content scales between any of them without distortion.
Why do all ISO paper sizes have a 1 : √2 aspect ratio?
It is the only ratio that stays the same when a sheet is folded or cut in half: a rectangle with sides \( w \) and \( w\sqrt{2} \) becomes \( \frac{w\sqrt{2}}{2} \) by \( w \), and \( \frac{w\sqrt{2}}{2} \times \sqrt{2} = w \). This means an A4 page enlarged by 141% (a factor of \( \sqrt{2} \)) fills an A3 sheet exactly, and photocopies never change their proportions.