Practical tools for measured work
Paper Size & Scale Calculator
Find the scale percentage to enlarge or reduce a document between standard paper sizes.
These two sizes share the same aspect ratio, so the scaled page fills the destination exactly.
How it works
How to use it: pick the paper size your original content is designed for and the paper size you want to print or photocopy it onto. The scale percentage is the number to enter on a photocopier or in your print dialog's "scale" field to make the content fit the new page.
Formula. The tool compares how much bigger or smaller the destination page is in each direction, then uses the more limiting one so nothing gets cropped: scale % = min(toWidth / fromWidth, toHeight / fromHeight) × 100. Every ISO 216 A-series size (A5, A4, A3…) shares the same proportions, so scaling between them is always a single clean number with no wasted margin; scaling to or from Letter, Legal or Tabloid - which use different proportions - fits the content fully but leaves a small margin on one side.
Worked example. A4 is 210 × 297 mm and A3 is 297 × 420 mm. Width ratio = 297 ÷ 210 = 1.4143; height ratio = 420 ÷ 297 = 1.4143 - identical, since both are A-series. Scale = 1.4143 × 100 ≈ 141.4%, the standard "enlarge A4 to A3" copier setting. Going the other way, A3 to A4, the ratios both come out to 210 ÷ 297 ≈ 0.7071, so the scale is ≈ 70.7% - the standard "reduce A3 to A4" setting.
Current-input example
The result above uses these exact values. This snapshot is included when the page is printed so the output can be checked against the original measurements.
- From paper size
- A4 (210 × 297 mm)
- To paper size
- A3 (297 × 420 mm)
Primary result: Scale to fit: 141.4 %.
Before using the result
- Measure from the datum or reference edge described by this tool, and do not mix inside, outside and centerline dimensions.
- Keep inputs in the displayed units and preserve more precision than the final cutting or purchasing tolerance requires.
- When the result is close to a limit, verify it with a test piece, field measurement, manufacturer drawing or qualified project professional.
Limitations
This computes the scale factor from nominal page dimensions only. It does not account for your printer or copier's non-printable margin, which can slightly clip content at the true 100% edge of a page - always preview or test-print for exact-fit work.
"Scale to fit" here means uniform (locked-aspect-ratio) scaling. It deliberately does not stretch content to fill a differently-proportioned page, since that would distort it.
Frequently asked questions
Why isn't the scale exactly 200% or 50% between some sizes?
Only adjacent A-series sizes work out to clean ratios in area (A3 has exactly double the area of A4), but the linear scale factor - the number your printer or copier actually uses - is the square root of that, about 141.4%, because area scales with the square of linear size.
Can I use this to scale a Letter document onto A4?
Yes - pick Letter as the from size and A4 as the to size. Because they have different proportions, the result fits the content without cropping but leaves a small margin on one edge rather than matching the page exactly.
Is this the same as the Print to Scale tool?
No - Print to Scale calibrates an image or drawing to a real-world physical measurement (e.g. so 1 inch on the printout equals 1 inch in reality). This tool instead converts between standard paper sizes at whatever scale fits, for copying or reformatting existing documents.
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