Explainer · metric paper sizes a0 to a4
Metric paper sizes A0 to A4 for drawings
By Sumana Kumar · Published 20 May 2023 · Updated 10 Mar 2025
The metric A-series paper sizes — A0, A1, A2, A3, A4 — are the standard sheets for technical drawings across most of the world. What makes them so useful is not any single size but the relationship between them: each size is exactly half the area of the one above, and they all share the same proportions, so a drawing reduces or enlarges cleanly between sheets without distortion. That single property simplifies plotting, copying and filing.
This explainer covers how the A series is built, the dimensions of each size, why the shared aspect ratio matters for drawings, and how to choose a sheet size to suit the scale you want to plot at.
How the A series is built
The A series starts from A0, defined to have an area of one square metre, and every smaller size is made by halving the longer side. Fold A0 in half across its long dimension and you get A1; halve A1 and you get A2, and so on down to A4 and beyond. Each step down halves the area while keeping the sheet the same shape.
This halving rule is the heart of the system. It means an A1 drawing photocopies neatly down to A2 or A3 at a known reduction, and an A4 page enlarges cleanly to A3. Nothing has to be cropped or stretched because every size in the series is geometrically similar to every other.
Dimensions from A0 to A4
In round figures, A0 is about 841 by 1189 mm, A1 about 594 by 841 mm, A2 about 420 by 594 mm, A3 about 297 by 420 mm, and A4 about 210 by 297 mm. Notice how the long side of each size becomes the short side of the next size up — A1's 841 long side is A0's 841 short side — which is the halving relationship made concrete.
These are the trimmed sheet sizes; drawings usually leave a margin and a binding edge inside them. The pattern is easy to remember: A4 is a familiar letter-ish page, and each step up roughly doubles it, so A0 is sixteen A4 sheets in area — a large drawing board's worth of paper.
Why the A series suits technical drawings
Technical drawings get reduced and enlarged constantly: a site plan issued at A1 for the office and A3 for site, a detail blown up for clarity, a set scanned and re-plotted. The A series handles all of this without distortion because of the shared ratio, so a drawing stays proportionally correct at every size.
It also files and folds cleanly. Larger sheets fold down to A4 for filing, and the predictable reductions make photocopying between sizes routine. Combined with a scale bar on the sheet, the A series means a drawing can travel between paper sizes and still be measured accurately — the bar reduces with the sheet, so the figures hold.
Choosing a sheet for your plot scale
Sheet choice flows from how much you need to draw and at what scale. A large building at 1:100 might need an A1 or A0 sheet to fit; a single detail at 1:5 fits comfortably on A3. The drawing's real-world extent divided by the scale ratio gives the size it occupies on paper, and you pick the smallest sheet that holds it with room for the title block and margins.
A practical approach is to set up a layout for the target sheet, place a viewport at the chosen scale, and see whether the drawing fits. If it spills off the sheet, either step up a size or split the drawing across sheets with a key plan to show how they relate. Keep the same scale across a set where you can, so a reader does not have to recalibrate between sheets.
A series and other standards
The A series is the ISO standard used for technical drawing in most countries. North American practice often uses a separate ANSI series with different proportions, so a drawing set up for A-series sheets does not map one-to-one onto letter, tabloid or ARCH sizes. If you are exchanging drawings across regions, agree the sheet standard up front to avoid awkward reductions.
Within the A series there are also elongated variants for long, thin drawings, but the everyday set is A0 down to A4. For most work, sticking to the A series across a project keeps plotting, folding and filing simple, and keeps every reduction and enlargement distortion-free.
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Questions
Frequently asked
What is special about A-series paper sizes?+
Each size is exactly half the area of the one above, and they all share the same proportions. That lets a drawing reduce or enlarge cleanly between sheets — A1 to A3, A4 to A3 — without cropping or stretching, which is ideal for technical drawings that get copied and re-plotted constantly.
What are the dimensions of A0 to A4?+
Roughly: A0 is 841 by 1189 mm, A1 is 594 by 841 mm, A2 is 420 by 594 mm, A3 is 297 by 420 mm, and A4 is 210 by 297 mm. The long side of each size is the short side of the next size up, which is the halving rule made concrete.
Why do all A sizes have the same shape?+
They share an aspect ratio of one to the square root of two, about 1:1.414. That is the only ratio that keeps its proportions when halved across the long side, so cutting any A sheet in two gives two sheets of the same shape. That is what preserves proportions down the whole series.
How do I pick a paper size for a drawing?+
Work out how much space the drawing occupies on paper — its real extent divided by the scale ratio — then pick the smallest A sheet that holds it with room for margins and a title block. If it won't fit, step up a size or split it across sheets with a key plan.
Are A-series sizes used everywhere?+
They are the ISO standard used in most countries, but North American practice often uses the ANSI series with different proportions. The two don't map one-to-one, so if you exchange drawings across regions, agree the sheet standard up front to avoid distorted reductions.
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