The Formulas
All of this is one relationship, rearranged three ways. Pixels, print size and DPI are three sides of the same equation:
| What you want | Formula | Example |
|---|
| Print size from pixels | pixels ÷ DPI = inches | 2400 ÷ 300 = 8 inches |
| Pixels from print size | inches × DPI = pixels | 8 × 300 = 2400 pixels |
| Effective DPI you end up with | pixels ÷ inches = DPI | 2400 ÷ 8 = 300 DPI |
| Megapixels | width × height ÷ 1,000,000 | 2400 × 3000 = 7.2 MP |
| Centimetres | inches × 2.54 | 8 × 2.54 = 20.3 cm |
300 DPI to Pixels: the Common Sizes
The question "how many pixels is 300 DPI" has no answer without a print size attached. Here are the sizes people ask about most:
| Print size | Pixels at 300 DPI | Megapixels |
|---|
| 4 × 6 in (10 × 15 cm) | 1,200 × 1,800 | 2.2 MP |
| 5 × 7 in (13 × 18 cm) | 1,500 × 2,100 | 3.2 MP |
| 6 × 9 in (KDP paperback) | 1,800 × 2,700 | 4.9 MP |
| 8 × 10 in (20 × 25 cm) | 2,400 × 3,000 | 7.2 MP |
| A4 (8.27 × 11.69 in) | 2,480 × 3,508 | 8.7 MP |
| 11 × 14 in (28 × 36 cm) | 3,300 × 4,200 | 13.9 MP |
| A3 (11.69 × 16.54 in) | 3,508 × 4,961 | 17.4 MP |
300 DPI in KB and MB
This is the question with the most misleading premise, so it is worth being blunt: DPI has no bearing on file size. The DPI tag is a handful of bytes of metadata. Change it from 72 to 300 and the file weighs the same to the byte.
What actually determines size is the pixel count and the compression. A rough guide for photographic content:
| Format | Roughly | 2400 × 3000 example |
|---|
| Uncompressed (24-bit) | width × height × 3 bytes | 21.6 MB |
| JPEG, quality ~85 | about one tenth of uncompressed | around 2 MB |
| PNG, photographic | about 40% of uncompressed | around 8.6 MB |
Treat the JPEG and PNG figures as ballpark. Flat graphics, screenshots and line art compress far better than photographs — a PNG of a simple logo might be a hundredth of these numbers.
Which DPI Do You Actually Need?
| Use | DPI | Why |
|---|
| Screens, web, email | Irrelevant | Displays work in pixels and ignore the tag entirely |
| Books, magazines, photo prints | 300 | The point where dots stop being distinguishable at reading distance |
| Large posters | 150–200 | Viewed from further away, so coarser dots go unnoticed |
| Billboards | 10–30 | Viewed from tens of metres away |
| Fine art and archival | 600 | Captures detail beyond what the eye resolves, for reproduction headroom |
The trap to avoid: a low DPI number does not mean a bad image. It means the file is carrying an instruction to print large. If the pixels are there, correcting the tag with our
DPI Converter is all it takes. If they are not, no tool can add them — you have to print smaller or start from a bigger original.
Frequently Asked Questions
How many pixels is 300 DPI?
DPI on its own is not a pixel count — you also need a print size. Multiply the size in inches by the DPI: 8 inches at 300 DPI is 2,400 pixels. An 8 by 10 inch print at 300 DPI therefore needs 2,400 by 3,000 pixels.
What size can I print a 2400 by 3000 pixel image?
Divide each side by your target density. At 300 DPI it prints 8 by 10 inches, which is 20.3 by 25.4 cm. At 150 DPI the same file covers 16 by 20 inches, but each dot is twice as coarse.
How many megapixels do I need for a 300 DPI print?
Multiply the pixel width by the pixel height and divide by one million. An 8 by 10 inch print at 300 DPI is 2,400 by 3,000 pixels, which is 7.2 megapixels. A 4 by 6 inch print needs only 2.2 megapixels.
How big is a 300 DPI image in KB or MB?
File size depends on compression, not on DPI. The DPI tag itself adds no weight at all. As a rough guide, a photographic JPEG lands near one tenth of its uncompressed size, and a PNG near 40 percent of it, so a 2,400 by 3,000 pixel photo is roughly 2 MB as a JPEG and 8 MB as a PNG.
Does changing the DPI number change the file size?
No. The DPI tag is a handful of bytes of metadata. Changing it from 72 to 300 alters the intended print size, not the pixels, so the file weighs the same before and after.
Is 72 DPI always too low for printing?
The number alone tells you nothing. What matters is pixels divided by printed size. A 6,000 pixel wide photo tagged 72 DPI has plenty of detail for a 20 inch print — it just carries the wrong instruction, which makes layout software place it far too large.
Related Reading
For the concepts behind these numbers, see What is DPI? and 72 DPI vs 300 DPI. If you are publishing on Amazon, the KDP image requirements guide covers the specifics.