Pixels to Print Size Calculator

Pixels divided by DPI gives you print size

A print size is pixel count divided by resolution. Take the width in pixels, divide it by the DPI you plan to print at, and you have the width in inches. Do the same with the height and you have the whole print. Photo labs run this exact division when they warn you that a file is too small for the size you ordered.

width in inches = pixels wide ÷ DPI
height in inches = pixels tall ÷ DPI

Two numbers control the result: how many pixels the file holds, and how many of those pixels get packed into each inch of paper. A 3000 pixel wide file printed at 300 DPI spreads 3000 pixels across 10 inches. The same file printed at 150 DPI spreads the same 3000 pixels across 20 inches, so every inch of paper receives half as many pixels.

That is why a photo can look sharp on a phone and soft on a poster. The file did not change. Only the number of pixels per inch of paper changed.

Worked example: a 3000 x 2400 photo at 300 DPI

Here is the arithmetic on a common 3000 x 2400 pixel photo, which is what a 12 megapixel camera produces.

• Width: 3000 ÷ 300 = 10.0 inches
• Height: 2400 ÷ 300 = 8.0 inches
• Print area: 10 x 8 = 80 square inches
• Metric: 10 x 2.54 = 25.4 cm wide, and 8 x 2.54 = 20.32 cm tall

At 150 DPI the same file gives 3000 ÷ 150 = 20 inches wide and 2400 ÷ 150 = 16 inches tall, which is 20 x 16 = 320 square inches. Doubling both dimensions multiplies the area by four, so the same pixels are stretched across four times as much paper.

At 600 DPI the file shrinks to 3000 ÷ 600 = 5 inches by 2400 ÷ 600 = 4 inches. Detail holds up, but the print is small. That is the trade every print makes: with a fixed pixel count, sharpness and size pull in opposite directions.

Why 300 DPI became the print benchmark

300 DPI is the number most labs, printers and publishers quote, and it is a rule of thumb rather than a law. It comes from the limit of human vision at reading distance: at roughly 300 pixels per inch, individual pixels stop being distinguishable on paper, so extra pixels mostly add file size.

Official digitization guidance lands in the same range. A 2013 post on the Library of Congress blog describes starting at 300 or 400 dpi when scanning documents for print. The U.S. Department of State sets a hard floor for passport photos in its digital image requirements: the printed photo must be exactly 2 x 2 inches (51 x 51 mm) and the digital image must be at least 600 x 600 pixels. Run the division and 600 ÷ 2 = 300, so a compliant passport photo is a 300 PPI file by definition.

Below 300 DPI prints still work. 150 DPI holds up on a poster seen from three feet away, and 72 DPI is fine for an image that only ever appears on a screen.

Pixel counts for common print sizes

If you know the print size you want, multiply each side by 300 to get the pixel count you need. The table below does that for standard photo and paper sizes, with the megapixel count that comes out.

Most phone cameras from the last few years land between 12 and 48 megapixels, so a 16 x 20 inch print is at the edge for a 12 megapixel phone and comfortable for a 48 megapixel one. Anything larger than 16 x 20 usually means a dedicated camera or a print lab that upscales the file before printing.

Watch the aspect ratio as well. A 3000 x 2400 file is 5:4, so it fits 8 x 10 exactly but has to be cropped to fill 4 x 6 or 5 x 7. Cropping throws pixels away, which lowers the resolution of whatever is left.

Enlarging a print lowers the real DPI

Print bigger than the file supports and the DPI falls. The math is the same division run in the other direction: pixel width divided by the new print width.

Each doubling of the print width halves the DPI, and halving the print width doubles it. A 3000 pixel file is 375 DPI at 8 inches, 187.5 DPI at 16 inches and 93.75 DPI at 32 inches. Nothing in the file degrades; the pixels are just spaced further apart.

Print software handles this in one of two ways. It can resample, inventing new pixels to fill the gaps, which keeps the file size up but cannot recover detail that was never captured. Or it can leave the pixels alone and let the printer spread them, which keeps the file honest and looks slightly softer. A lab that asks for a 300 DPI file at 24 x 36 inches is asking you for 7200 x 10800 pixels.

PPI, DPI and the 72 DPI myth

Pixels live in the file. Dots live on the paper. A printer that sprays 1440 dots per inch is not printing a 1440 PPI file, because each pixel is built from a grid of several ink dots. When a spec sheet says 5760 x 1440 dpi, that is the printer's droplet grid, not the resolution your photo needs.

The 72 DPI figure that shows up in image metadata is a leftover from early Macintosh screens, where one inch of screen equaled 72 pixels. Some cameras and editors still write 72 into the file, and that number has no effect on how the file prints. Only two things matter: the pixel dimensions, and the print size you choose. A 3000 pixel wide file tagged 72 DPI prints at exactly the same size as the same file tagged 300 DPI.

Screen resolution works the same way. A 3000 pixel image on a 3000 pixel wide display fills the screen at 1:1. On a 1500 pixel wide display it is shown at 50% and looks crisp. The pixel count did not change, and neither did the file.

Four checks before you order a print

The calculator gives you a size. These four checks catch the problems it cannot see.

• Compare pixels to the ordered size, not to the screen. A file that fills your monitor can still be short of pixels for a 20 x 30 inch canvas. Divide the pixel width by the print width and ask whether the answer is above 150.
• Check the crop. Standard frames are 8 x 10 (5:4) and 11 x 14 (about 4:5), while most cameras shoot 3:2. Fitting a 3:2 file into 8 x 10 crops the long side, which throws away about 17% of the width and lowers the effective DPI on the short side.
• Match DPI to viewing distance. A 24 x 36 inch print on a hallway wall is viewed from four feet or more, where 100 to 150 DPI reads as sharp. A 4 x 6 inch print in your hand is viewed at about a foot, where 300 DPI earns its keep.
• Ask the lab what it wants. Some labs resample anything under 300 DPI and charge for it, and some reject files under 150 DPI for large formats. A two minute check saves a reprint.

A 12 megapixel phone photo is enough for 8 x 10 at 300 DPI (7.2 MP needed) and enough for 16 x 20 at 150 DPI (7.2 MP needed at that size as well, since halving the DPI quarters the pixel requirement).

Megapixels, file size and the limits of upscaling

Megapixels are just width times height divided by one million. A 4000 x 3000 file is 4000 x 3000 = 12,000,000 pixels, or 12 MP. At 300 DPI that file prints 4000 ÷ 300 = 13.3 inches by 3000 ÷ 300 = 10 inches.

Upscaling software can double the pixel count and fill the gaps with interpolated detail. It helps a print look smoother at close range, and it cannot add information the lens never captured. A 6 MP file upscaled to 24 MP is still a 6 MP file in terms of real detail, and the print will show it at 300 DPI on a 16 x 20.

File size is a separate question. A JPEG at 300 DPI for an 8 x 10 print is often 2 to 5 MB, while the same dimensions saved as a TIFF can run 30 MB or more. For prints up to 11 x 14, a high quality JPEG is usually indistinguishable from a TIFF. For a 24 x 36 inch canvas, the extra data in a TIFF or a raw file is worth keeping.

One last habit: keep the original. Every crop, resize and re-save of a JPEG costs a little quality, and the losses stack. Work from the original file each time you order a new size, and the numbers on this page will keep matching what comes back from the lab.