Methods & precision

Units and arithmetic

One inch is exactly 25.4 mm, or 2.54 cm. Physical-to-pixel calculations use integer rational arithmetic for the final nearest or upward rounding, avoiding spurious extra pixels from floating-point conversion at exact boundaries. Other geometric calculations use JavaScript double-precision numbers; displayed rounding does not feed back into the calculations.

Accepted inputs

Image dimensions accept whole pixels from 1 to 100,000 per axis. Physical lengths accept 0.01 to 10,000 in the chosen unit, with at most four decimal places. PPI accepts 1 to 10,000 with four decimal places. Crop ratio components accept whole numbers from 1 to 1,000. Margins accept 0 to 1,000 in the selected unit and must leave a positive usable area. These broad computational limits are not printer capabilities.

Quick conversions and CSS

The quick measurement converter permits zero and fractional values up to 100,000,000, with four decimal places. It returns an unrounded measurement rather than choosing an integer canvas. Its CSS mode fixes 96 CSS px per CSS inch. CSS unit conversions accept signed values from −100,000 to 100,000, font references from 0.01 to 1,000 CSS px and viewport references from 1 to 100,000 CSS px, all to four decimal places. rem uses the root font; em uses the supplied font reference; vw and vh use the supplied large viewport dimensions. These dimensions are entered explicitly, never inferred from screen hardware.

Rounding and geometry

Nearest pixel rounds positive half pixels upward. Round up means ceiling each axis. A proportional resize rounds the unconstrained side to the nearest pixel and reports the resulting ratio difference. Exact crops are integer multiples of the reduced ratio; an odd leftover pixel is removed from the right or bottom. Fit preserves the full image; fill clips the centered image to the usable rectangle.

Output precision

Result headings and measurements show up to two decimals unless a more precise value is useful. Detailed results, copied values and CSV results show up to six decimals. Input values retain the precision you entered, up to the accepted limits. Paper size conversions display three decimals. Small nonzero measurements use up to three significant digits when the usual decimal precision would hide them; CSV and copied results use the same rounding as the detailed values. All diagrams show proportions, never calibrated physical size.

Sharing and files

Share links store validated numbers and options in a URL fragment. Fragments are not included in the HTTP request to this server, but anyone you send the link to can read the numbers. Local image bytes and filenames are not included. Images are decoded by the browser with orientation metadata applied; JPEG, PNG and WebP are accepted up to 12 MiB and 60 million decoded pixels. A file is never resized or cropped for download.

What the calculations do not establish

We do not assess photographic detail, printer compatibility, color management, paper quality, bleed requirements or acceptable viewing distance. The screen tool assumes a rectangular panel with square native pixels. Use a provider’s actual requirements and inspect a proof when the result matters.