PPI Calculator
Calculate the pixels per inch your image will print at, and the largest quality print size.
Last updated · View algorithm, constants and default inputs (JSON)
About this calculator
Compare image pixels with print dimensions to estimate effective pixels per inch (PPI). Quality bands are rough reference points, not guarantees; viewing distance, printer, paper and image content affect perceived detail.
Worked example
calculated with the default values below
Image width 6,000 px · Image height 4,000 px · Print width 20 in · Print height 13.3 in · Target quality 300 ppi — gallery quality PPI across the width 300.0 ppi · PPI across the height 300.1 ppi · Effective PPI 300.0 ppi · Print quality Excellent — gallery quality · Largest print at target quality 20.00 in · Largest print at target quality 13.33 in · Megapixels 24.0 MP
General background references
Disclaimer
These calculators give general estimates. Sizing, pricing, availability and standards vary by brand, retailer and country, so treat the output as a starting point and confirm it against the seller's or authority's own figures.
Implementation source
This record describes the implementation used by this page. It is not independent validation. External references, when available, support only the stated formula or definition; estimates and custom rules retain their own assumptions.
Formula and variables
PPI = min(W ÷ pw, H ÷ ph); L = W ÷ Pt; MP = W × H ÷ 10⁶
- W
- Image width (px)
- H
- Image height (px)
- pw
- Print width (in)
- ph
- Print height (in)
- Pt
- Target PPI
- MP
- Megapixels
Horizontal PPI = image width / print width; vertical PPI = image height / print height; effective PPI is the lower value. Quality bands are approximate guidance, not a universal sharpness threshold.
Frequently asked questions
Why does effective PPI take the smaller of width and height?
The calculator reports ppi on each axis and keeps the lower value as effective, because sharpness is capped by the weaker dimension. At the 300 target the largest print width is simply image width divided by 300; drop the target to 150 and that ceiling doubles, and to 72 it quadruples for poster viewing. Changing the target quality select therefore rescales the largest-print answer directly, while a mismatched print ratio lets the shorter axis fall below the chosen ppi first.