Paper Size Calculator — A4 to Letter Scale %

The Scale Percentage for A4 to Letter

94%. That is the number you type into the print dialog to fit an A4 document onto US Letter paper. Going the other way — Letter onto A4 — is 97%.

The reason it is not obvious is that neither sheet is simply bigger. A4 is 210 × 297 mm; Letter is 215.9 × 279.4 mm. A4 is narrower but taller. So A4 onto Letter is limited by height (279.4 ÷ 297 = 0.94), while Letter onto A4 is limited by width (210 ÷ 215.9 = 0.97). Each direction is constrained by a different edge, which is exactly why people misremember it.

The diagram above shows both sheets overlaid at true relative scale, so you can see which edge is doing the cutting rather than taking the number on faith.

ISO A Series Scaling

The A series has a property that makes this easy: every size is the previous one halved across its long edge, so the ratio between any two adjacent sizes is always √2 ≈ 1.414.

One size down (A3→A4, A4→A5, A2→A3) — 71%
One size up (A4→A3, A5→A4, A3→A2) — 141%
Two sizes down (A2→A4, A3→A5) — 50%
Two sizes up (A4→A2, A5→A3) — 200%

Those four figures cover every A-series conversion — A3 to A4 scale conversion included — which is why photocopiers have exactly those buttons. The same ratios drive blueprint scale conversion, since architectural sheets follow the same series. It also means an A-series document never crops when scaled between A sizes — the proportions are identical. That is not true of any A-to-US conversion.

Paper Size Chart in mm

Paper size chart: ISO A, B and US sizes in millimetres and inches
Size	Millimetres	Inches	Standard
A0	841 × 1189	33.11 × 46.81	ISO A
A1	594 × 841	23.39 × 33.11	ISO A
A2	420 × 594	16.54 × 23.39	ISO A
A3	297 × 420	11.69 × 16.54	ISO A
A4	210 × 297	8.27 × 11.69	ISO A
A5	148 × 210	5.83 × 8.27	ISO A
A6	105 × 148	4.13 × 5.83	ISO A
Letter	215.9 × 279.4	8.50 × 11.00	US
Legal	215.9 × 355.6	8.50 × 14.00	US
Tabloid	279.4 × 431.8	11.00 × 17.00	US
Executive	184.15 × 266.7	7.25 × 10.50	US
B4	250 × 353	9.84 × 13.90	ISO B
B5	176 × 250	6.93 × 9.84	ISO B

This paper size chart gives mm and inches for every common sheet. ISO A and B sizes are defined by ISO 216; US sizes are shown to two decimal places in millimetres because they are defined in inches — Letter is exactly 8.5 × 11 in.

Getting the Print Right

Turn off "Fit to page". It silently scales to your printer's unprintable margin, which is not the same as your chosen percentage, and it is the usual reason a printout comes out slightly small.
Set the scale manually to the number above.
Check the paper size setting matches the paper actually in the tray. A mismatch here overrides everything else.
Measure the result if the size matters — for a sewing pattern, a scale drawing, or anything that will be cut. Printers apply their own margin handling on top of your setting.

When Scaling Is the Wrong Answer

For sewing patterns, technical drawings, and anything printed to a stated scale, do not scale at all. Print at 100% on the correct paper size, or print across multiple sheets and join them. A pattern printed at 94% produces a garment 6% too small in every dimension, and you will not discover that until it is cut.

Most such documents include a test square — usually 10 cm or 1 inch — precisely so you can verify the scale before cutting. Print one page, measure the square, and only continue when it is exact.

Frequently Asked Questions

How do I print A4 on Letter size paper?

Scale to 94% in your print dialog. A4 is 210 mm wide and Letter is 215.9 mm, but A4 is 297 mm tall against Letter's 279.4 mm — so height is the binding constraint. 279.4 ÷ 297 = 0.94. At 100% the bottom 18 mm of your A4 page would be cut off.

What size is A4 compared to Letter?

A4 is narrower and taller. A4 is 210 × 297 mm; Letter is 215.9 × 279.4 mm. So A4 is about 6 mm narrower and 18 mm taller. Neither fits inside the other without scaling, which is why documents crossing between them always need a percentage.

Is A4 the same as Letter size?

No, though they are close enough that the difference is easy to miss until something is cut off. A4 is the ISO 216 international standard used almost everywhere; Letter is the North American standard. A4 is taller, Letter is wider.

What percentage do I scale A3 to A4?

71%. Every step down the ISO A series is the same ratio — 1 ÷ √2, or about 0.7071 — because each size is the previous one halved across its long edge. That is what makes A3 to A4, A4 to A5, and A2 to A3 all exactly 71%.

What percentage do I scale A4 to A3?

141%. It is the inverse of the 71% reduction — √2, or about 1.4142. The same figure enlarges A5 to A4 and A3 to A2, since the ratio between adjacent ISO A sizes is constant.

Does A4 fit on Legal paper?

Yes, at 100%. Legal is 215.9 × 355.6 mm — wider and considerably taller than A4's 210 × 297 mm — so an A4 page fits inside it with room to spare. You will have a large blank margin at the bottom unless you scale up to 103%, which is limited by width — Legal is only 5.9 mm wider than A4, so there is little room to grow.

Why is my printout slightly smaller than it should be?

Almost always because the print dialog has 'Fit to page' or 'Shrink to fit' enabled, which silently scales to the printer's unprintable margin. Turn it off and set the percentage manually. Also set scaling to 100% before measuring anything printed for reference.

How do I check my printer actually scaled correctly?

Print a page with a known measurement on it and check it with a ruler. Printers apply their own margin handling on top of your scale setting, so the only reliable verification is measuring the result. Our online ruler works for this if you have no physical one to hand.