DPI and Print Size Calculator (Pixels to Inches, Both Ways)

Pixels to printed size and back, at whatever resolution you choose — plus the part that actually decides the job: whether the file is big enough. The thresholds here are derived from ISO 12647-2’s own screen-ruling range and from one arcminute of visual acuity, and the page says which of the two each number comes from.

Last updated 24 Sep 2026

Pixels, print size and resolution

Pixels ↔ inches, with an honest verdict

What are you working out?

Image width (pixels)

Image height (pixels)

Print size units

Print width

Print height

Target resolution (ppi)300 ppi is twice a 150 lines-per-inch halftone screen, which is mid-range for coated stock under ISO 12647-2. It is a screen ruling doubled, not a law of optics.

Pixels on the long edge as CAPTURED, before any upscalingLeave this equal to the long edge above unless you have resized the file upwards. Resampling to more pixels adds no detail, so the effective resolution stays set by the original capture.

Viewing distance (mm)Reading distance is 300 to 400 mm; a poster on a wall is 1,000 to 3,000. This drives the acuity figure, which is the only part of this page with a measurement behind it.

Not a circuit: the same pixel count printed at 96, 150, 240 and 300 pixels per inch, drawn to scale from one corner. The rectangles are exact whatever your pixel count, because their sizes are in the ratio of the reciprocals of the resolutions — 1 : 0.64 : 0.4 : 0.32 — and that ratio does not depend on the file. The figure inside each is your own long edge at that resolution. Note how little area separates 240 from 300, and how much separates 96 from 150: resolution buys size in inverse proportion, so the last step costs the most and shows the least.

300.0ppiExample

a 3,000 × 2,000 px file printed 10 inches on the long edge

One division, and two published thresholds

inches = pixels ÷ ppi · effective ppi = pixels as CAPTURED ÷ inches · halftone rule: ppi = 1.5 to 2 × screen ruling in lpi · acuity limit: ppi = 87,319 ÷ viewing distance in mm

pixels as captured: the long-edge pixel count of the original file, before any resampling. Upscaling changes the first term of the division and not the detail, which is why this page separates the two
1.5 to 2: the published quality factor: an image needs one and a half to two samples per halftone line to use a screen fully. ISO 12647-2 allows 48 to 80 lines per centimetre (122 to 203 lpi), so the factor puts the useful range at 183 to 406 ppi, and 300 is exactly twice a 150 lpi screen
87,319: 25.4 mm per inch divided by the tangent of one arcminute. One arcminute is the minimum angle of resolution for 20/20 vision, so this constant divided by the viewing distance in millimetres is the finest detail per inch a normally-sighted reader can separate
ppi against dpi: ppi is samples in the image; dpi is marks the device makes. An inkjet quoting 1,200 dpi lays many dots per image pixel and does not want a 1,200 ppi file

Worked example

a 3,000 × 2,000 px file printed 10 inches on the long edge
3,000 px ÷ 10 in = 300 ppi, and the short edge gives 2,000 ÷ 6.6667 = 300 too, so the aspect matches
300 ppi is twice a 150 lines-per-inch screen, which is 59 lines per centimetre — mid-range for coated stock under ISO 12647-2's 48-to-80 cm⁻¹ allowance
At the 400 mm viewing distance set here, 20/20 vision resolves 218 ppi, so this print carries 137% of what the eye can separate
The same file at 240 ppi would print 12.5 in on the long edge, and at 150 ppi it would print 20 in
Uncompressed at 8 bits per channel it is 18 MB, which is what the resolution costs

What ISO 12647-2 allows, and what the quality factor then asks for

The screen rulings are ISO 12647-2:2013 clause 4.2.3: 48 to 80 lines per centimetre for coated paper and 48 to 70 for uncoated. The lpi and ppi columns are computed here. This is where 240 and 300 ppi come from — 240 is twice the coarsest screen the standard allows, 300 is twice a 150 lpi screen — and it is also why the standard itself states no image resolution: clause 4.2.2 sets a plate-setter resolution and stops.
Stock and screen	Screen ruling	lpi	ppi at factor 1.5	ppi at factor 2
Uncoated, coarsest allowed	48 cm⁻¹	121.9	183	244
Uncoated, typical	60 cm⁻¹	152.4	229	305
Uncoated, finest allowed	70 cm⁻¹	177.8	267	356
Coated, typical	60 cm⁻¹	152.4	229	305
Coated, finest allowed	80 cm⁻¹	203.2	305	406

What the eye can resolve, by viewing distance

Computed from one arcminute as the minimum angle of resolution for 20/20 vision, which is the Snellen definition. The assumption is stated because it is doing all the work: a reader with better than 20/20, or one who leans in, moves the whole column. Note that a billboard read from ten metres needs under 9 ppi — which is why billboards are printed at resolutions that would be absurd on a page.
Distance (mm)	Distance (in)	ppi at 20/20 acuity	Screen it supports	Where that is
250	9.8	349.3	174.6	close reading, a held book
300	11.8	291.1	145.5	normal reading distance
400	15.7	218.3	109.1	a magazine on a desk
500	19.7	174.6	87.3	a monitor, or a large book
1,000	39.4	87.3	43.7	a poster you walk up to
2,000	78.7	43.7	21.8	a poster across a room
3,000	118.1	29.1	14.6	a display board
10,000	393.7	8.7	4.4	a billboard from the pavement

Camera resolutions and the size they print at four resolutions

Long edge × short edge in inches, computed here. The column that surprises people is 300 ppi: a 24-megapixel camera prints 20 × 13.3 in at 300 ppi, so the megapixel race has been irrelevant to A3 prints for over a decade. What limits a big print is almost always the lens, the focus and the subject movement, not the sensor count.
Sensor	Pixels	at 150 ppi	at 240 ppi	at 300 ppi	at 360 ppi
2 MP	1600 × 1200	10.7 × 8.0 in	6.7 × 5.0 in	5.3 × 4.0 in	4.4 × 3.3 in
8 MP	3264 × 2448	21.8 × 16.3 in	13.6 × 10.2 in	10.9 × 8.2 in	9.1 × 6.8 in
12 MP	4032 × 3024	26.9 × 20.2 in	16.8 × 12.6 in	13.4 × 10.1 in	11.2 × 8.4 in
24 MP	6000 × 4000	40.0 × 26.7 in	25.0 × 16.7 in	20.0 × 13.3 in	16.7 × 11.1 in
45 MP	8256 × 5504	55.0 × 36.7 in	34.4 × 22.9 in	27.5 × 18.3 in	22.9 × 15.3 in
61 MP	9504 × 6336	63.4 × 42.2 in	39.6 × 26.4 in	31.7 × 21.1 in	26.4 × 17.6 in

The division is trivial. The judgement is the page.

Inches are pixels divided by resolution, and that is the last easy thing about it. A 3,000 px edge is 10 in at 300 ppi, 12.5 in at 240 and 20 in at 150. The question nobody’s calculator answers is which of those you are allowed to do, and the honest answer has two halves: what the printing process can use, and what the eye can see. They give different numbers, and the larger of the two is the one that binds.

The press half has a real standard behind it, indirectly. ISO 12647-2:2013, which is the process-control standard for offset litho, sets the halftone screen ruling in clause 4.2.3: 48 to 80 lines per centimetre for coated paper and 48 to 70 for uncoated, which is 122 to 203 lines per inch. It says nothing at all about image resolution — clause 4.2.2 specifies the plate-setter and stops — so any “standard” of 300 ppi is not in the standard. What connects the two is the trade’s quality factor: an image needs one and a half to two samples per halftone line to use the screen fully. Put the factor and the ruling together and the useful band is 183 to 406 ppi. 300 ppi is exactly twice a 150 lpi screen, which is a normal coated-stock ruling; 240 ppi is exactly twice the coarsest screen the standard allows. That is the whole provenance of both figures, and it means the difference between 240 and 300 is a question about your printer’s screen, not about quality in the abstract.

The eye half is a measurement, and it is more forgiving than people expect. Normal visual acuity — 20/20, or 6/6 — is defined as a minimum angle of resolution of one arcminute. Convert that to a resolution and you get 87,319 divided by the viewing distance in millimetres: 291 ppi at 300 mm, 218 ppi at 400 mm, 87 ppi at a metre, 44 ppi at two metres. So 300 ppi is roughly the acuity limit for something held at reading distance, which is why it feels like a natural ceiling for a book or a brochure — and why 150 ppi is genuinely sufficient for a poster nobody stands closer than a metre to. Both figures fall out of the same arcminute.

Upscaling. Resampling a 1,000 px image to 3,000 px triples the pixel count and adds no information: the interpolation invents values between the samples you already had, so the finest real detail is still the one the capture recorded. Print that file at 10 inches and the nominal resolution reads 300 ppi and the effective resolution is 100. This page asks for the original capture separately and puts the effective figure in the headline, because the nominal one is the number that gets people into trouble. Modern machine-learning upscalers are better at guessing plausible detail, which is a different claim from recording it.

And ppi is not dpi. Pixels per inch counts samples in your image; dots per inch counts marks the device makes. An inkjet at 1,200 dpi is laying many small ink dots to build each image pixel’s tone, and feeding it a 1,200 ppi file wastes everything past about 300 to 360. A laser printer’s 600 dpi is likewise a marking resolution. The only place the two coincide is a continuous-tone device such as a dye-sublimation printer. For the named paper sizes these prints go onto, see the paper size converter, which also gives every ISO and US sheet in pixels; for the stock itself, the paper weight converter.

Frequently asked questions

Is 300 dpi a standard?

No standard states it. ISO 12647-2 fixes the halftone screen ruling at 48 to 80 lines per centimetre and says nothing about image resolution. 300 ppi is twice a 150 lpi screen, on the trade’s quality factor of 1.5 to 2 samples per halftone line — so it is a convention with an arithmetic derivation, not a measured threshold. Ask your printer what screen they run and the right figure falls out.

Is 240 ppi good enough for print?

Usually yes. 240 ppi is exactly twice the coarsest screen ISO 12647-2 permits, and at normal reading distance it is above what 20/20 vision resolves at 350 mm. The visible difference between 240 and 300 ppi on a magazine page is very small; the difference between 150 and 240 is not.

What resolution does a poster need?

It depends on how close people get, and nothing else. At one metre, 20/20 vision resolves about 87 ppi; at two metres, about 44. So 150 ppi is comfortable for a poster read from a metre and generous from further. Large-format printers are often happiest with 100 to 150 ppi at final size, and a billboard read from ten metres needs under 9 ppi.

Does upscaling an image help?

It does not add detail. Interpolation fills in between the samples you captured, so the finest real detail is unchanged and only the file grows. That is why this page asks for the original capture and reports the effective resolution: a 1,000 px file resampled to 3,000 px and printed at 10 in is a 100 ppi print wearing a 300 ppi label. Upscaling does sometimes help the printer’s own resampling behave better, and modern machine-learning upscalers guess convincingly — but guessing is not recording.

What is the difference between dpi and ppi?

ppi is samples per inch in your image; dpi is dots per inch the device puts down. A 1,200 dpi inkjet uses many ink dots per image pixel to make a tone, so it does not want a 1,200 ppi file. The terms are used interchangeably everywhere, including in this page’s title, because that is what people search for — but they are different quantities.

How big can I print a 24-megapixel photograph?

6,000 × 4,000 px prints 20 × 13.3 in at 300 ppi, 25 × 16.7 in at 240 and 40 × 26.7 in at 150. In practice the sensor stops being the limit long before that: focus accuracy, lens resolution, diffraction at small apertures and subject movement all bite first.

Why does my image say 72 dpi?

Because that is a tag in the file’s metadata, not a property of the pixels. 72 was the old Macintosh screen resolution and is also the PostScript point, so it became a default. A 3,000 × 2,000 px file tagged 72 dpi contains exactly the same information as one tagged 300; changing the tag without resampling changes nothing but the size the software suggests.

Related calculators

References

ISO 12647-2:2013, Graphic technology — Process control for the production of half-tone colour separations, proof and production prints — Part 2: Offset lithographic processes, clause 4.2.3: the screen frequency for periodic screens “should be within the range from 48 cm⁻¹ to 80 cm⁻¹” for coated paper and 48 to 70 cm⁻¹ for uncoated. Read from the publicly posted ISO preview at cdn.standards.iteh.ai. Those are 122 to 203 and 122 to 178 lines per inch, and they are where the 240 and 300 ppi figures on this page come from. Clause 4.2.2 sets a plate-setter resolution and says nothing about input image resolution, which is the honest reason no standard states a ppi.
Wikipedia, Lines per inch (read 26 September 2026), for the quality factor: “in order to effectively utilize the entire range of available LPI in a halftone system, an image selected for printing generally must have 1.5 to 2 times as many samples per inch”, with 150 lpi × 2 = 300 dpi given as the worked case, newsprint quoted at about 85 lpi and coated magazine stock up to 300 lpi.
M. Kalloniatis and C. Luu, Visual Acuity, in H. Kolb, E. Fernandez and R. Nelson (eds), Webvision: The Organization of the Retina and Visual System, University of Utah (webvision.pitt.edu, read 26 September 2026): “for a visual acuity of 6/6 (20/20), one of the strokes of the letter subtends one minute of arc at the eye. Therefore, the minimum angle of resolution (MAR) is one minute of arc.” That one arcminute is the only assumption behind every viewing-distance figure on this page.
W3C, CSS Values and Units Module Level 4 (w3.org/TR/css-values-4/ and the editor’s draft at drafts.csswg.org, read 26 September 2026) — a public specification, quoted directly. It fixes 1in = 96px, 1pt = 1/72in, 1pc = 12pt and 1px = 1/96in; defines em as “the computed value of the font-size property of the element on which it is used”, and notes that in the font-size property itself it resolves against the size inherited from the parent; defines rem as “the computed value of the em unit on the root element”; and defines ex as the used x-height and ch as the advance measure of the “0” glyph — both font metrics, which is why this page refuses them. It also gives the fallbacks the spec mandates when those metrics are unavailable: “a value of 0.5em must be assumed” for ex.
National Institute of Standards and Technology, Refinement of Values for the Yard and the Pound, Federal Register notice of 1 July 1959, which fixed the international inch at exactly 25.4 mm and the avoirdupois pound at exactly 0.45359237 kg. Both exact values are used throughout this batch; every inch-to-millimetre figure here is therefore exact, not approximate.