Digital images have no physical size until you decide how many pixels to place in each inch of paper. At 300 pixels per inch (the long-standing benchmark for photo prints held at reading distance) a 6,000 × 4,000 image covers 20 × 13.3 inches; at 150 PPI the same file stretches to 40 × 26.7 inches with visibly softer detail up close.
The right PPI depends mostly on how far away the print will be seen. Normal vision resolves about one arcminute, which works out to roughly 3,438 ÷ distance in inches. A photo-book page at 30 cm needs close to 290 PPI, a poster on a wall seen from 2 m needs about 45 PPI, and a billboard seen from 50 m needs only a couple of pixels per inch.
This calculator works in three directions: from your image to the largest sensible print, from a paper size to the pixels you need (for example when cropping or ordering a scan), and from an image plus a paper size to the effective PPI the lab will print at, with a quality verdict.
How to use the Pixels to Print Size Calculator
- I want to find
- Image width
- Image height
- Print resolution: 300 for photo prints, 240 for good quality, 150 for posters
- Print size
- Custom print width
- Custom print height
- Orientation
- Viewing distance
Results update as you type, every field has its own unit menu, and everything is calculated in your browser.
How it works
Choose what you want to find. Print dimensions are pixels divided by PPI; required pixels are inches multiplied by PPI. For the effective PPI the image’s long side is matched to the paper’s long side and the smaller of the two ratios is reported, because that is the side that limits sharpness when the print is filled.
Worked example
A 6,000 × 4,000 image at 300 PPI prints at 6,000 ÷ 300 = 20 in by 4,000 ÷ 300 = 13.33 in (50.8 × 33.87 cm). To print a 4R (4 × 6 in) photo at 300 PPI you need 4 × 300 = 1,200 by 6 × 300 = 1,800 px. Placing the 6,000 × 4,000 image on A3 (11.69 × 16.54 in) gives min(6,000 ÷ 16.54, 4,000 ÷ 11.69) = min(362.8, 342.1) = 342 PPI (excellent), with 5.7% of the image cropped to match the paper shape. Seen from 0.5 m (19.7 in), the eye resolves about 3,438 ÷ 19.69 = 175 PPI.
Recommended PPI by viewing distance
| Viewing distance | PPI the eye resolves (1′) | Typical use |
|---|---|---|
| 0.3 m (12 in) | 286 | Photo books, held prints |
| 0.5 m (20 in) | 175 | Desk prints, A4 |
| 1 m (39 in) | 87 | Framed photos on a shelf |
| 2 m (79 in) | 44 | Posters on a wall |
| 5 m (16 ft) | 17 | Large banners |
| 50 m (164 ft) | 1.7 | Billboards |
Inputs explained
| Field | What to enter |
|---|---|
| I want to find | Choose one: The print size of my image, The pixels needed for a print size, The print resolution of my image on a paper size |
| Image width | In px |
| Image height | In px |
| Print resolution | In PPI. 300 for photo prints, 240 for good quality, 150 for posters |
| Print size | Choose one: 2R (2.5 × 3.5 in, wallet), 3R (3.5 × 5 in), 4R (4 × 6 in, standard photo), 5R (5 × 7 in) … |
| Custom print width | Units: in, cm, mm |
| Custom print height | Units: in, cm, mm |
| Orientation | Choose one: Portrait (short side horizontal), Landscape (long side horizontal) |
| Viewing distance | Units: m, cm, mm, km, in, ft … |
What each result means
- Print width = [Image width]÷[Print resolution]×0.0254
- Print height = [Image height]÷[Print resolution]×0.0254
- Megapixels needed = [Pixels needed: width]×[Pixels needed: height]÷1e6
- Effective print resolution = min(max([Image width], [Image height])÷([Paper long side (m)]÷0.0254), min([Image width], [Image height])÷([Paper short side (m)]÷0.0254))
- Image cropped away to fill the paper = (1 – min((max([Image width], [Image height])÷min([Image width], [Image height]))÷([Paper long side (m)]÷[Paper short side (m)]), ([Paper long side (m)]÷[Paper short side (m)])÷(max([Image width], [Image height])÷min([Image width], [Image height]))))×100
- Megapixels = [Image width]×[Image height]÷1e6
- PPI your eyes can resolve at this distance = 3438÷([Viewing distance]÷0.0254)
- PPI for very sharp eyes (½ arcminute) = 6876÷([Viewing distance]÷0.0254)
Formula
Print width = width (px) ÷ PPI · Pixels needed = print size (in) × PPI · Effective PPI = min(long side px ÷ long side in, short side px ÷ short side in) · PPI needed ≈ 3438 ÷ viewing distance (in) for 1 arcminute
Worked example
Inputs: I want to find: The print size of my image; Image width: 6,000 px; Image height: 4,000 px; Print resolution: 300 PPI; Viewing distance: 0.5 m.
Results: Print width = 20 in; Print height = 13.33 in; Megapixels = 24 MP; PPI your eyes can resolve at this distance = 175 PPI; PPI for very sharp eyes (½ arcminute) = 349 PPI.
Key terms
- PPI
- Pixels per inch, how densely image pixels are placed on the paper.
- DPI
- Dots per inch, the density of ink dots a printer lays down.
- Effective PPI
- The PPI an image actually prints at for a given paper size.
- Arcminute
- 1/60 of a degree; roughly the smallest detail normal vision resolves.
Frequently asked questions
How big can I print a 12 MP photo?
A 4,000 × 3,000 image prints at 13.3 × 10 in (34 × 25 cm) at 300 PPI, or 26.7 × 20 in at 150 PPI for a poster.
How many pixels do I need for a 4 × 6 in print?
1,200 × 1,800 px at 300 PPI (2.16 MP).
How many pixels do I need for A4 at 300 PPI?
2,481 × 3,508 px (A4 is 210 × 297 mm = 8.27 × 11.69 in), about 8.7 MP.
Is 300 PPI always necessary?
No. 300 PPI suits prints held in the hand. Wall prints seen from 1–2 m look sharp at 100–150 PPI, and billboards use 10 PPI or less.
Are PPI and DPI the same?
PPI counts image pixels per inch; DPI counts the printer's ink dots, which are much finer. Print labs often say "DPI" when they mean PPI.
What if my image has a different shape from the paper?
The lab crops (fill) or adds borders (fit). The calculator shows how much of the image a fill crop removes.
Does upscaling help a low-resolution print?
Modern AI upscalers can make edges cleaner, but they cannot recover detail that was never captured.