DPI vs PPI, explained for people who sell art
· 6 min read
PPI describes your file and DPI describes the printer. Pixels per inch is how many image pixels land in each inch of the print; dots per inch is how many ink dots the machine sprays. Everyone, including your print provider, says DPI for both — and that is almost always fine. Here is when it is not.
What PPI actually is
Your image file is a grid of pixels. A photo that is 2400 by 3000 pixels has exactly that many, and no more, forever. Nothing about the file says how big it should be printed.
PPI appears the moment you decide. Spread those 2400 pixels across 8 inches and you get 300 pixels per inch. Spread the same 2400 pixels across 16 inches and you get 150 PPI — same file, same pixels, different physical density, and a visibly softer print.
So PPI is not a property of the file. It is a property of the file plus a decision about size. This is the single most useful thing to understand here, because it explains why “is this photo high resolution?” has no answer until someone says how big it is being printed.
What DPI actually is
DPI belongs to the printer. An inkjet builds each image pixel out of many tiny overlapping ink dots, because a single dot can only be one colour of ink — to make a specific shade of golden-retriever brown it has to dither several dots together.
That is why printer specifications quote numbers like 1200 or 2400 DPI while you are being asked for a 300 PPI file. They are not the same measurement and they are not in conflict. Roughly four to eight printer dots go into reproducing one image pixel.
Why nobody keeps them straight, and why that is okay
Print-on-demand services ask for “300 DPI files”. Etsy sellers talk about “300 DPI artwork”. Photoshop’s dialog says Resolution and then labels the units pixels/inch. The words have blurred, and in practice the meaning is unambiguous: when someone asks for a 300 DPI file, they mean 300 pixels per inch at the finished print size.
You can use their vocabulary without confusion. The distinction only becomes load-bearing in one situation, below.
The one situation where the difference bites
Files carry a DPI tag in their metadata, and it is just a note — a stored number saying what physical size the file was intended for. It has no effect on image quality and does not change a single pixel.
But many print-on-demand services read that tag and size the print from it. So:
- A 2400x3000 file tagged 300 DPI describes an 8x10 inch print. Correct.
- The same 2400x3000 file tagged 72 DPI describes a 33x42 inch print. The service may scale it to fit whatever you ordered, or it may reject it, or it may print it enormous and soft.
The pixels are identical in both cases. Only the note differs, and the note is what the machine reads. This is why setting the DPI metadata correctly on export is worth caring about even though it changes nothing about the image.
The trap in Photoshop’s Image Size dialog
In Image Size there is a Resample checkbox, and it changes what typing “300” into the Resolution field does.
- Resample off: changing Resolution only rewrites the tag and recalculates the print dimensions. No pixels change. This is free and correct, and it is what you want.
- Resample on: changing Resolution invents new pixels to hit the number. The file gets bigger, the tag says 300, and there is not one scrap of extra detail — just a larger, softer image that now claims to be print-ready.
That second one is how “I set it to 300 DPI” turns into a soft print and a refund request. The number in the metadata went up. Nothing else did.
How many pixels you actually need
Multiply the print size in inches by 300. That is it. The table below is the arithmetic already done for every size worth selling.
| Print size | Inches | Pixels at 300 DPI | Pixels at 200 DPI | Camera needed |
|---|---|---|---|---|
| 5x7" | 5 × 7 | 1,500 × 2,100 | 1,000 × 1,400 | 3.1 MP |
| 8x8" | 8 × 8 | 2,400 × 2,400 | 1,600 × 1,600 | 5.8 MP |
| 8x10" | 8 × 10 | 2,400 × 3,000 | 1,600 × 2,000 | 7.2 MP |
| A4 | 8.27 × 11.69 | 2,481 × 3,507 | 1,654 × 2,338 | 8.7 MP |
| 11x14" | 11 × 14 | 3,300 × 4,200 | 2,200 × 2,800 | 14 MP |
| 12x12" | 12 × 12 | 3,600 × 3,600 | 2,400 × 2,400 | 13 MP |
| 12x16" | 12 × 16 | 3,600 × 4,800 | 2,400 × 3,200 | 17 MP |
| A3 | 11.69 × 16.54 | 3,507 × 4,962 | 2,338 × 3,308 | 17 MP |
| 16x20" | 16 × 20 | 4,800 × 6,000 | 3,200 × 4,000 | 29 MP |
| 18x24" | 18 × 24 | 5,400 × 7,200 | 3,600 × 4,800 | 39 MP |
| 24x36" | 24 × 36 | 7,200 × 10,800 | 4,800 × 7,200 | 78 MP |
When 300 is more than you need
The 300 figure comes from roughly the limit of what a human eye resolves at typical reading distance, about 30 centimetres. Prints are not all viewed at reading distance, and the requirement falls with distance:
- Held in the hand or on a desk — 5x7, 8x10: aim for 300.
- On a wall, viewed from a metre or two — 11x14 to 18x24: 200 is genuinely fine.
- Large, viewed across a room — 24x36: 150 will pass.
Conveniently, print size and viewing distance rise together, which is the only reason large prints are possible at all.
The exception, which matters here
Fur breaks the rule. Individual strands and whiskers are near-single-pixel features, and unlike a landscape’s gradual tones they are high contrast against their neighbours. When resolution runs short, fur does not go gently soft — it smears into a texture that reads as felt.
So bias upward for close crops of an animal’s face even at large sizes, and relax for full-body poses where the animal occupies less of the frame.
The short version
- Your file has pixels. Everything else is a decision about how to spread them.
- PPI is that decision. DPI is the printer’s business.
- Say DPI like everyone else. Nobody will misunderstand you.
- Do set the DPI tag correctly on export — print services read it.
- Never “increase the DPI” by resampling. It adds a number, not detail.
- Check the pixels against the size before you promise anything. That is the only number that cannot be faked.