To make sure your prints come out sharp, detailed and professional, check your image file before you upload it. Three things decide the result: the resolution, the colour profile and the file size.
1. Resolution (DPI)
DPI means dots per inch. It tells you how many pixels your file has for every inch of the finished print. This is the single biggest factor in how sharp your print looks.
Printumo produces print files at two different resolutions:
Fine art paper prints: 300 DPI. Paper prints are viewed close up, so they need the higher resolution.
Canvas prints: 150 DPI. The texture of the canvas softens fine detail, and canvas is normally viewed from further away, so 150 DPI is enough.
To work out the pixels you need, use this formula: pixels = (centimetres ÷ 2.54) × DPI.
For example, a 30 x 40 cm fine art paper print needs 3,543 x 4,724 pixels. The same size printed on canvas needs 1,772 x 2,362 pixels.
Pixel sizes for every fine art paper size
If you would rather look the number up than work it out, here is every fine art paper size we print and the pixels it needs at 300 DPI. The figures are for a portrait print (width x height). Turn them around for a landscape print.
A6 (10.5 x 14.8 cm): 1240 x 1748
A5 (14.8 x 21 cm): 1748 x 2480
A4 (21 x 29.7 cm): 2480 x 3508
A3 (29.7 x 42 cm): 3508 x 4961
A2 (42 x 59.4 cm): 4961 x 7016
A1 (59.4 x 84.1 cm): 7016 x 9933
20 x 20 cm: 2400 x 2400
20 x 25 cm: 2400 x 3000
20 x 30 cm: 2400 x 3600
30 x 40 cm: 3543 x 4724
40 x 40 cm: 4724 x 4724
40 x 50 cm: 4724 x 5906
40 x 55 cm: 4500 x 6300
50 x 50 cm: 5906 x 5906
50 x 70 cm: 5906 x 8268
60 x 90 cm: 7200 x 10800
70 x 70 cm: 8268 x 8268
70 x 100 cm: 8268 x 11811
100 x 100 cm: 11811 x 11811
100 x 140 cm: 11811 x 16535
Aim to match these figures or to sit a little above them. A file that lands exactly on the number is right on the boundary of the top grade.
A few sizes are sold in inches rather than centimetres: 8 x 12", 12 x 16", 18 x 24" and 24 x 36". For those, multiply the inch figure by 300. A 24 x 36" print needs 7200 x 10800 pixels.
2. The quality dot in the product editor
You do not have to do the calculation yourself. After you upload your artwork, every print size shows a coloured dot. The dot tells you how well your file performs at that size.
Fine art paper
Dark green (great): 300 DPI or more
Green (good): 200 to 299 DPI
Amber (average): 150 to 199 DPI
Red (poor): under 150 DPI
Canvas
Dark green (great): 150 DPI or more
Green (good): 75 to 149 DPI
Amber (average): 50 to 74 DPI
Red (poor): under 50 DPI
The dots inform you, they do not block you. You can still offer a size that shows an amber or a red dot, but we recommend that you do not.
The grade is worked out from the detail your file really holds, not from its pixel count alone. A file that was enlarged in another tool before you uploaded it carries more pixels than detail, so it is graded as the smaller original it came from. When that happens the dot shows a note that reads "Enlarged before upload".
This is why two files with the same pixel size and the same DPI can show different dots. An enlargement shows most in pictures with smooth surfaces and soft gradients, which hold less fine detail than busy ones. The measurement is the same every time, so uploading the same file again gives the same dot.
When a dot is amber or red, we may offer to fix it
If a size shows an amber or a red dot, Printumo may offer to rebuild your artwork with our AI Upscaler before it is printed. It costs you nothing extra, your original file is never changed, and the rebuild happens when an order comes in rather than at upload.
If you say yes, the dots for the sizes we can improve change colour straight away, often from amber to green. They now show the quality the rebuilt file will print at. Your uploaded file has not been changed. Hover over a dot and its label ends in "After upscaling". To see the grade of your own file again, click "Use original artwork instead" above your print sizes.
The offer only appears when a rebuild would genuinely lift the quality of a size you are offering. If it does not appear, your file does not hold enough real detail to rebuild from, and a smaller print size is the better answer.
For the full explanation, see How the AI Upscaler works.
3. Colour profile
Use the sRGB colour profile. sRGB is the standard for print on demand, and it keeps your colours consistent across screens and prints.
Other profiles are accepted. Adobe RGB has a wider gamut, and CMYK files work too, but both can shift in colour when they are converted. Convert your file to sRGB before you upload it to avoid surprises.
Everything is printed in sRGB. Whatever profile you send, we convert it to sRGB for printing.
4. File size
File size on its own tells you very little, because it depends on the file format and the compression as much as on the pixels. Use the pixel dimensions above as your guide instead. Two limits are still worth knowing:
A very small file, for example under a few MB for a large print, usually means low resolution or heavy compression.
Uploads are capped at 150 MB, and at 100 MB for PDF. A file above that limit is not a better file. It is normally uncompressed, layered, or saved at 16 bits per channel, and none of that reaches the paper.
Quick checklist before you upload
Does the file have enough pixels for the largest size you want to sell? Use 300 DPI for paper and 150 DPI for canvas.
Is the colour profile sRGB?
Is the file a flattened JPEG, PNG, TIFF or PDF, and under the size limit?
Are the quality dots green for every size you plan to offer?
Need help checking your file?
If you are unsure about your file, send a message to Printumo Support with the file attached. Our team will review it for you before you launch your product.