Photography Calculators

Sensor & focal length

Megapixel Print Size Calculator

Megapixels set how many pixels you have; aspect ratio splits them into width and height; DPI says how large that can print before the lab is interpolating. 300 DPI is a close-view photo print. 150 DPI is a wall you stand back from. This is not a quality score — a 24 MP file printed huge still needs a sharp file.

Inputs

Units
MP

Effective stills megapixels, not the video pixel count.

3 for 3:2, 4 for 4:3, 16 for 16:9.

2 for 3:2, 3 for 4:3, 9 for 16:9.

DPI

300 for close album prints. 240 is common inkjet. 150 for large wall pieces.

Results

Width
6,000px
Height
4,000px
Print width
20.00in
Print height
13.33in
Print width
50.8cm
Print height
33.9cm

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Calculation method

Total pixels are megapixels times one million. Split them in the aspect ratio: width in pixels is the square root of (total pixels times width/height), height is width times height/width. Print inches are those pixels divided by DPI. Centimetres are inches times 2.54. A 24 MP 3:2 file at 300 DPI is about 20×13 inches (51×34 cm) before the lab crops to paper.

Exact formula

widthPx = √(MP×1e6 × aspectW/aspectH). heightPx = widthPx × aspectH/aspectW. inches = px/DPI. cm = inches × 2.54. Limits: Printer margins, resampling quality and viewing distance omitted; no ‘maximum print’ marketing claim.

PPI vs DPI

On screen it is PPI; on a printer it is DPI. For this tool they are the same ratio: pixels per inch of output. Your monitor’s 110 PPI does not cap the print.

Borderless paper

A 4×6 print is 3:2. A 5×7 or 8×10 is not — the lab will crop. Check the aspect-ratio crop calculator before you compose tight.

Frequently asked questions

Is 300 DPI mandatory?

For a book held at arm’s length, 250–300 is the usual lab request. A 1.5 m canvas viewed from two metres can look fine at 150. Viewing distance matters more than a round number.

Does cropping waste megapixels?

Yes. A 16:9 crop from 3:2 throws away pixels — see aspect-ratio crop. Recalculate MP after the crop if you care about the print.

Upsampling in the lab?

Labs will stretch pixels. That is not the same as having them. This calculator reports native size at the DPI you type, with no interpolation.

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