Will it print sharp enough
Pick the print you want and see whether your file has the pixels for it — at the distance that print will actually be seen from — plus what cropping to a different shape costs.
How big is it going?
Bigger prints are looked at from further back, so they need fewer pixels per inch than people assume.
Step 2 — your file—
How many frames fit on a card
Where the thresholds come from
300 pixels per inch is the printing industry's habit, taken from what a person with good eyesight can resolve at about 25 cm. It is the right target for something held in the hand and the wrong one for something on a wall.
Viewing distance is conventionally taken as the print's diagonal, and the resolution needed falls in proportion — so this page asks for 300 ppi on a small print, 240 on a mid-sized one, 180 on a large one and 120 on a poster. A billboard at 20 ppi looks perfect from across the street.
The figure reported is the lower of the two edges' resolutions after cropping to the print's shape, because that is the one you would see.
Print resolution is a question about viewing distance
The single most common mistake is applying 300 ppi to everything. It is the right target for something held in the hand — a book, a 6×4, a portfolio print you lean over. It is a wasteful target for a print that will hang on a wall and be looked at from two metres, where 150 ppi is indistinguishable from 300 and the file you already have is fine.
The rule of thumb built into this page is that people view a print from roughly its diagonal. It is approximate, but it is far closer to how prints are actually seen than a fixed number.
Aspect ratio is where the pixels really go
Most cameras shoot 3:2. Almost no common print size is 3:2. An 8×10 is 5:4, so printing a 3:2 file at 8×10 discards a fifth of the frame before anything else happens — and it comes off the long edge, which is usually where the composition was. Square-ish print sizes are the worst offenders.
If you know a picture is destined for an 8×10, frame it loose. The crop figures above show exactly what each shape costs.
Related
To actually perform the resize or crop, use resize images or compress to an exact size — both run locally in the same way.
Questions people actually ask
Do I really need 300 ppi?
Only for prints held in the hand. 300 ppi is a printing convention, not an optical limit — what the eye resolves depends on viewing distance, and larger prints are viewed from further away. A 24×36 at 150 ppi looks perfect on a wall. Billboards run around 20 ppi.
Why does an 8×10 crop so much off my photo?
Because your camera shoots 3:2 and an 8×10 is 5:4. The shapes do not match, so a fifth of the frame has to go, and it comes off the long edge. This is why 8×10 prints so often cut something important — the composition was made in a wider rectangle.
Can I upscale to make a bigger print?
Up to a point. Modern upscalers, including the machine-learning kind, do a much better job than simple interpolation, but they are inventing plausible detail rather than recovering real detail. Doubling linear dimensions is usually fine; quadrupling shows. A print that is marginal at native size will not become sharp by being enlarged.
Why does my 64GB card hold less than 64GB?
Two reasons, both boring. The card is sold in decimal gigabytes — 64,000,000,000 bytes — while your computer counts in binary ones, which makes it about 59.6 GiB, roughly 7% less. Then the filesystem takes a little more. The figure above accounts for this.
Why do my raw files vary so much in size?
Because raw compression is content-dependent. A detailed forest holds far more information than an empty sky, and the file can differ by half again between the two on the same camera. Any capacity figure is an average, which is why this one is labelled an estimate.