The Plaid Studio / Print sizes / DPI calculator

DPI calculator

Three questions, one rule — pixels = inches × DPI. How many pixels a print needs, how large a file you already have will print, and what DPI an image works out to at a given size. In centimetres or inches, for fabric, paper and print-on-demand.

How many pixels do I need?

Width Height Unit DPI

Pixels

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Megapixels

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At 300 DPI

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How large will my file print?

Width (px) Height (px) DPI

Print size (cm)

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Print size (in)

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At 300 DPI

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What DPI is my image at this size?

Width (px) Printed width Unit

Effective DPI

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Verdict

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The rule behind it

Pixelspixels = inches × DPI, and an inch is 2.54 cm. So pixels = cm ÷ 2.54 × DPI: 20 cm at 150 DPI is 1181 px.
Print sizeinches = pixels ÷ DPI. A 3000 px file prints 20 inches (50.8 cm) wide at 150 DPI and 10 inches at 300.
150 DPIWhat fabric printers and most apparel print-on-demand ask for. Spoonflower prints every file at 150.
300 DPIPaper, stationery, mugs and anything seen in the hand. Printful asks 300 for posters and non-apparel.
DPI or PPIStrictly, PPI describes the file and DPI the printer. Print-on-demand specs use DPI for both, and so does this page.

For a seamless pattern, the size that matters is one repeat, not the product: a 20 cm tile repeated down a roll of fabric needs 1181 px at 150 DPI however long the roll is. The print-on-demand pixel sizes page lists product-by-product sizes, and the DPI guide explains what each service asks for.

Make a pattern at the right size Check a pattern is seamless

Questions

How many pixels is 300 DPI?

It depends on the print size: multiply the size in inches by 300. An A4 page (21 × 29.7 cm, 8.27 × 11.69 in) at 300 DPI is 2480 × 3508 pixels; a 20 cm square is 2362 × 2362.

Is 150 DPI good enough for printing?

For fabric, apparel and wallpaper, yes: they are seen from arm's length or further, and most fabric printers print at 150. Paper, stationery and products seen in the hand look better at 300.

How do I convert centimetres to pixels?

Divide by 2.54 to get inches, then multiply by the DPI. 30 cm at 300 DPI is 30 ÷ 2.54 × 300 = 3543 pixels.

Does changing the DPI in an image editor add detail?

No. Changing the DPI setting only changes how large the same pixels will print. To print larger at the same quality you need more pixels — export the pattern again at the bigger size.