Print size and DPI

A print’s size is its pixels divided by its resolution: 6000 pixels at 300 pixels per inch is 20 inches. How much resolution you need depends on how close people stand: the page works that out from how fine a detail the eye can see.

Units switch sizes between centimetres and inches (remembered for all the photography tools). Resolution is always in pixels per inch, as printers and labs quote it.

How to use it

Size — type the image’s width and height in pixels (or pick a common sensor) and a resolution. The cards give the print size, the megapixels, the aspect ratio and the distance from which that resolution looks perfectly sharp; the table repeats it from 72 to 360 ppi.
Viewing distance — the resolution worth printing for a viewing distance, and the largest print your pixels make at it. Acuity is 1 arcminute for normal vision; set 0.5 for very sharp eyes or a picky client.
Crop to paper — pick a paper (ISO A sizes, inch sizes and metric photo sizes). Fill crops the photo to the paper’s shape and shows what’s cut off; drag the photo or the slider to move the crop. Fit keeps the whole photo with white borders. Drop or choose a photo to see the overlay on it; it stays on your device. The cards give the resolution on that paper, how much of the photo survives, the crop in pixels and the upscaling needed to reach your target resolution.
Mat & frame — the mat window (the print less the overlap that holds it), the outer size for your border width and any extra at the bottom, the smallest standard US (inch) or European (cm) frame that fits it, and the borders that result. A drawing shows them to scale.

Where the numbers come from

Acuity. Normal (20/20 or 6/6) vision resolves about 1 arcminute — the stroke width of a Snellen letter on the 20/20 line. Detail finer than that at the viewing distance can’t be seen: ppi = 1 ÷ (distance × tan 1′) ≈ 3438 ÷ distance in inches. At 10 inches (25 cm, reading distance) that is about 344 ppi, which is where the habit of 300 ppi comes from; at 1 m it is 87 ppi.
Viewing distance of about 1.5–2 times the print’s diagonal is a rule of thumb for how far people stand to take in a whole picture.
Paper sizes: ISO 216 (A series, in mm) and the usual North American and metric photo sizes.
Mats: a window overlapping the print by about ¼ inch (6 mm) a side, 2–3 inch (5–8 cm) borders and "bottom weighting" are framers' conventions, not standards.

Limits

Acuity is for high-contrast detail under good light; most photographs show less, so prints below these numbers often look fine. Upscaling software adds pixels, not detail.
Printer DPI (ink dots per inch) is not image ppi; leave the printer driver’s resolution to the driver.
Standard frame sizes vary by shop and country; check the frame’s rebate (the inner lip) and the mat’s real size before cutting.

Related: depth of field and lenses (sensor sizes and the circle of confusion, which assumes a print size and distance), exposure calculator, EXIF statistics.

Linking to an example

Share link copies a URL that opens the tool with your settings (never the photo you dropped). Links can also be written by hand; put the tab after #: size, view, crop or mat. Lengths in links are always in inches.

Parameter Meaning Example

Parameter	Meaning	Example
`w` / `h`	Image width and height in pixels	`w=6000&h=4000`
`ppi`	Resolution for the Size tab	`ppi=300`
`paper`	Paper id: `a4`, `a3`, `a3+`, `8x10`, `letter`, `13x19`, `30x40` …	`paper=a3`
`mode`	`fill` (crop) or `fit` (borders)	`mode=fit`
`margin`	White margin round the print, inches	`margin=0.5`
`pos`	Crop position, 0 (left or top) to 1 (right or bottom)	`pos=0.5`
`want`	Target resolution for upscaling, ppi	`want=300`
`dist`	Viewing distance, inches	`dist=40`
`border`	Mat border, inches	`border=2.5`
`weight`	Extra mat at the bottom, inches	`weight=0.5`
`overlap`	Mat overlap onto the print, inches	`overlap=0.25`
`frames`	Frame sizes: `in` (US) or `cm` (European)	`frames=cm`
`example`	One of the presets below; parameters given with it override the preset’s	`example=a3-crop`

w / h

Image width and height in pixels

w=6000&h=4000

ppi

Resolution for the Size tab

ppi=300

paper

Paper id: a4, a3, a3+, 8x10, letter, 13x19, 30x40 …

paper=a3

mode

fill (crop) or fit (borders)

mode=fit

margin

White margin round the print, inches

margin=0.5

pos

Crop position, 0 (left or top) to 1 (right or bottom)

pos=0.5

want

Target resolution for upscaling, ppi

want=300

dist

Viewing distance, inches

dist=40

border

Mat border, inches

border=2.5

weight

Extra mat at the bottom, inches

weight=0.5

overlap

Mat overlap onto the print, inches

overlap=0.25

frames

Frame sizes: in (US) or cm (European)

frames=cm

example

One of the presets below; parameters given with it override the preset’s

example=a3-crop

Presets:

example= Shows

`example=`	Shows
`24mp-300`	A 24 MP (6000 × 4000) photo at 300 ppi prints 20 × 13⅓ in (50.8 × 33.9 cm) (open)
`a3-crop`	A 3:2 photo filling A3 (√2:1): 94 % of it is kept, at about 342 ppi (open)
`billboard`	A print seen from 3 m (118 in) needs only about 29 ppi (open)
`mat-8x10`	An 8 × 10 in print with 2 in borders: a 7½ × 9½ in window, in a 12 × 16 in frame (open)

24mp-300

A 24 MP (6000 × 4000) photo at 300 ppi prints 20 × 13⅓ in (50.8 × 33.9 cm) (open)

a3-crop

A 3:2 photo filling A3 (√2:1): 94 % of it is kept, at about 342 ppi (open)

billboard

A print seen from 3 m (118 in) needs only about 29 ppi (open)

mat-8x10

An 8 × 10 in print with 2 in borders: a 7½ × 9½ in window, in a 12 × 16 in frame (open)