Print Size Calculator

What it does

Converts between pixels and physical print size using one number — dots per inch (dpi), how many pixels the printer lays down per inch of paper. Pixels ÷ dpi = inches; inches × dpi = pixels. The first card takes your file's dimensions and gives the print size at a chosen dpi plus the largest print it can make at each common quality level; the second takes a print size and gives the pixels it needs, and tells you what resolution your file would actually deliver at that size.

What you'll need

• Your image's pixel width and height — from the file's properties, the EXIF Viewer, or your editor's export dialog.
• A print resolution in dpi (300 is the photo-lab default).
• For the reverse, the print size you have in mind, in inches or centimetres.

Steps

1. Enter the file's pixel width and height and pick inches or centimetres.
2. Read the print size at your chosen dpi and the largest-print table underneath.
3. In the second card, enter the print size you actually want to make and read the pixels needed — and the dpi your file delivers at that size.

Reading the result

The largest-print table is the useful one: it shows how big the file goes before the effective resolution drops below each threshold. 300 dpi is for prints looked at in the hand; 200 is sharp on a wall at arm's length; 150 is fine across a room. If the second card says your file delivers less than you hoped, either print smaller, accept that a large print is viewed from further away, or upsample in your editor — which adds pixels but never adds detail.

Tips

• Viewing distance is the real variable. A 30 × 45 cm print at 200 dpi on a wall looks every bit as sharp as a 10 × 15 cm at 300 dpi in the hand, because nobody puts their nose on a wall print.
• The pixel count is what matters — the dpi a file 'says' it is (72, 240, 300) is a label in the metadata, not a property of the pixels. Change the number and nothing about the image changes.
• For a lab order, match their stated dpi (usually 300) and give them the pixel size from the second card; for a home inkjet, 240 dpi is the point where more pixels stop making a visible difference.

What is print resolution (dpi)?

A digital image has no physical size — it's a grid of pixels. It only gains a size in inches or centimetres when you decide how densely to lay those pixels onto paper, and that density is the print resolution: dots (pixels) per inch, dpi, or its metric cousin pixels per centimetre. The same 6000 × 4000 px file is a 20 × 13 inch print at 300 dpi and a 40 × 27 inch print at 150 dpi — identical pixels, different spacing.

Strictly, dpi describes the printer's ink dots and ppi (pixels per inch) describes the image, and an inkjet lays down many ink dots per image pixel. In everyday use — and in this calculator — the two are used interchangeably to mean image pixels per printed inch, because that's the number labs and export dialogs ask for.

Why photographers use it

Every print order, every gallery wall and every 'can this go big?' question comes down to this arithmetic. Get it right and you know exactly how large a file can go before it softens, whether an older camera's files still make a decent 40 × 60 cm, and how many pixels to ask a client for. Get it wrong and the lab either rejects the file or quietly upsamples it — and a print that looked sharp on screen arrives soft.

Which dpi should I aim for?

300 dpi for anything held in the hand or examined closely — photo books, small prints, portfolios, competition entries. 240 dpi is the practical ceiling for most inkjet printers; beyond it the extra pixels are invisible. 200 dpi for wall prints viewed from a normal standing distance. 150 dpi for large prints seen across a room, and as low as 100 dpi for banners and posters at several metres. Pick the lowest dpi the viewing distance allows and you'll be surprised how large a modest file can go.

Common mistakes

• Changing the dpi field in an editor and expecting a sharper print. the dpi stored in a file is a label. Setting a 3000 px wide file to 300 dpi instead of 72 changes its nominal print size from 41 inches to 10, but the pixels are the same 3000 — nothing got sharper, the number just tells the printer to space them more tightly.
• Judging a wall print by the 300 dpi rule. 300 dpi is a hand-viewing standard. Insisting on it for a 60 × 90 cm print demands a 7000 × 10000 px file for sharpness nobody will ever stand close enough to see. Use the viewing distance to pick the target.
• Upsampling to hit a lab's minimum and thinking the problem is solved. upsampling invents pixels between the real ones. It stops a lab from rejecting the file and can smooth the pixel grid, but it adds no detail — a soft original becomes a large soft print.
• Cropping first, checking size later. a heavy crop can halve the pixel width, and pixel width is what sets the maximum print size. Check the cropped file's dimensions, not the camera's megapixel count.
• Forgetting the aspect ratio. a 3:2 camera file doesn't fit a 4:5 or A-series print without cropping or borders. Decide which before you calculate — the pixels you have for a 20 × 25 cm print are the pixels left after the crop to 4:5, not the whole frame.

Example settings

FAQ

Is dpi the same as ppi?

Not strictly — ppi is image pixels per inch, dpi is printer ink dots per inch — but labs, printers and export dialogs use them interchangeably to mean the same thing, and so does this calculator.

What dpi do photo labs want?

Most ask for 300 dpi at the final print size, and many will accept down to 150 for large prints. When in doubt, use the second card to get the pixel size at 300 and check your file meets it.

Does a higher dpi make the print sharper?

Only if you have the pixels to supply it. Dpi is the spacing of the pixels you already have; more pixels per inch means a smaller print, not a sharper one. Sharpness comes from the capture and the file's real detail.

Why does the 'largest print' table go down as the dpi goes up?

Because you're dividing the same pixel count by a larger number. A fixed file gets physically smaller the more tightly its pixels are packed — that's the whole trade-off between print size and resolution.

Do I need to upload a photo?

No — this is pure arithmetic on numbers you type in. If you don't know your file's pixel size, the EXIF Viewer reads it from the file in your browser.