Will it print sharp enough
What a print actually needs at the distance it will be seen from, what a crop to a different shape costs you, and how many frames fit on a card.
Print size and crop
What the crop costs
Printing a 3:2 file at 8×10 means throwing pixels away. This is how many.
Card capacity
Nothing leaves this device
Where the thresholds come from
ppi = pixels ÷ print inches
The familiar 300 ppi is a printing-industry convention, not a property of the eye. What the eye can resolve depends on how far away it is, and prints are viewed at distances that scale with their size — nobody presses their nose to a poster. So the target here falls as the print grows: 300 ppi up to about a 14-inch diagonal, 240 to 30 inches, 180 to 50, and 120 beyond that.
That is why billboards print at 20 ppi and look perfect from the road. It is also why a 24-megapixel file that is marginal at 300 ppi for a 24×36 print is entirely adequate in practice — you will stand back to look at it.
Card capacity is an estimate for two reasons. Cards are sold in decimal gigabytes and formatted in binary ones, which costs about 7% before a single file is written. And raw file size varies with subject detail — a forest compresses worse than a clear sky, sometimes by half again.
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.