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Photo Size Calculator
Our free photo size calculator — also a print size calculator — tells you exactly how large a photo will print, or how many pixels you need for the print size you want. Enter the width and height in pixels, pick a DPI, and see the print size in inches, centimeters, and millimeters, plus megapixels and aspect ratio. Switch to the reverse mode to work out the pixels a target print size needs. Everything runs in your browser; your photo never leaves your device.
No photo uploaded — type the dimensions below.
Pixels across.
Pixels down.
Print width.
Print height.
Unit for the print size.
Dots per inch.
Or pick a preset.
How it works
A digital photo is a grid of pixels; a print is that grid spread across paper. DPI — dots per inch — is the bridge between the two: it says how many pixels are packed into each inch of the printed page. To find the print size, divide the pixels by the DPI. A photo 6000 pixels wide printed at 300 DPI comes out 6000 ÷ 300 = 20 inches wide; 4000 pixels tall comes out 4000 ÷ 300 = 13.33 inches tall. The pixels are the same; they are simply spread thinner.
The reverse mode runs the same idea backwards. If you know the print size you want, multiply it by the DPI to get the pixels you need. An 8 × 10 inch print at 300 DPI needs 8 × 300 = 2400 pixels wide and 10 × 300 = 3000 pixels tall. If your photo is smaller than that, print it smaller, accept a lower DPI and a softer print, or let the print shop upscale it — which adds no real detail. This calculator shows the shortfall plainly, so you can decide before you pay for a print.
Megapixels are the total pixel count in millions: width × height ÷ 1,000,000. A 6000 × 4000 photo holds 24,000,000 pixels, which is 24 megapixels. The aspect ratio describes the shape of the photo, reduced to its simplest whole numbers by dividing both sides by their greatest common divisor. 6000 × 4000 reduces to 3:2, the classic shape of a camera photo, while 4000 × 4000 is 1:1, a square.
The DPI you choose depends on how the print will be viewed. 300 DPI is the standard for a sharp photo print or anything held in the hand, and it is what print shops ask for. 150 DPI suits a poster or a large print seen from a few feet away, where the eye cannot pick out fine detail. A photo that looks huge on screen can still be too small for a good print.
The file size estimates are a rough guide, not an exact count. They use typical compression for an ordinary photograph: about 0.25 bytes per pixel for JPEG at quality 80, about 0.45 bytes per pixel for JPEG at quality 90, about 0.22 bytes per pixel for WebP, and about 1.5 bytes per pixel for PNG, which compresses photos poorly. A busy photo compresses less than a simple one, so the real file can be larger or smaller than the estimate.
Worked example
Suppose your camera saved a photo that is 6000 pixels wide and 4000 pixels tall, and you want a high-quality print at 300 DPI.
Step 1: choose "Pixels → print size" and enter 6000 for the width and 4000 for the height — or upload the photo and let the tool read them.
Step 2: set the DPI to 300 and click Calculate.
Step 3: the tool reports a print size of 20 × 13.33 inches. Here is the working: 6000 ÷ 300 = 20 inches wide, and 4000 ÷ 300 = 13.33 inches tall. In metric units that is 50.8 × 33.87 centimeters.
Step 4: Megapixels: 6000 × 4000 = 24,000,000 pixels, which is 24 megapixels. Aspect ratio: divide both sides by 2000 and 6000 × 4000 becomes 3:2. The file size guide estimates about 6.0 MB as a JPEG at quality 80, about 10.8 MB at quality 90, and about 36.0 MB as PNG.
Now try the reverse. Switch to "Print size → pixels" and ask for an 8 × 10 inch print at 300 DPI. The tool reports 2400 × 3000 pixels — 7.2 megapixels — because 8 × 300 = 2400 and 10 × 300 = 3000. Your photo has more than enough pixels for that print, and the tool notes it also fits the standard sizes 4 × 6, 5 × 7, and 8 × 10 at 300 DPI. A 24 × 36 inch poster at 300 DPI would need 7200 × 10800 pixels, which your photo does not have — so print that poster at 150 DPI, where it needs only 3600 × 5400 pixels, and still looks good from a few feet away.
FAQ
What is DPI and why does it matter for printing?
DPI stands for dots per inch: how tightly the pixels of your photo are packed on the printed page. A photo of 3000 by 2000 pixels printed at 300 DPI comes out 10 by 6.67 inches, because 3000 divided by 300 is 10. At 150 DPI the same photo prints twice as wide, 20 by 13.33 inches, but softer, because each inch holds half as many pixels. DPI does not change the pixels in the file — only how large they are printed.
What DPI should I use for a good print?
Use 300 DPI for a sharp photo print, a book, or anything viewed up close — that is the standard print shops ask for. Use 150 DPI for a poster or a large print viewed from a few feet away. Use 72 DPI only for screens. Printing a screen-resolution image at 300 DPI gives a very small print, so check your pixels before you order.
How many megapixels do I need for a print?
Multiply the print size in inches by the DPI you want to get the pixels you need on each side. A 4 by 6 inch print at 300 DPI needs 1200 by 1800 pixels, about 2.2 megapixels. An 8 by 10 inch print needs 2400 by 3000 pixels, about 7.2 megapixels. A 16 by 20 inch print at 300 DPI needs 4800 by 6000 pixels, about 28.8 megapixels — more than many cameras shoot, so large prints are often made at 150 DPI instead.
Does uploading my photo send it anywhere?
No. When you choose a photo, your browser reads it on your own device and the file is never uploaded to a server. Only the width and height in pixels are used, and the photo itself is never sent anywhere or stored. You can also skip the upload and just type the pixel dimensions by hand.
Why are the file size estimates only approximate?
JPEG, PNG, and WebP all compress the image, and how much they can squeeze it depends on what is in the picture. A photo of a clear blue sky compresses far smaller than a photo of a busy crowd. The estimates here use typical compression for an ordinary photo, so treat them as a rough guide, not an exact byte count.