Print Resolution Calculator

The core idea behind this calculator is that print resolution needs scale down as viewing distance grows -- a billboard viewed from across a highway doesn't need photo-lab DPI, while a wallet photo held a foot from your face does. Required DPI comes from a fixed visual- acuity constant (3438, roughly one radian in arcminutes, paired with the eye's ~1-arcminute resolving limit) divided by Viewing Distance converted to inches, so it falls sharply as Viewing Distance rises: moving from a 2-foot viewing distance to a 10-foot one drops the DPI requirement from roughly 143 down to about 29. Viewing Distance is the sole driver of Required DPI -- Print Width and Print Height never enter that formula at all, so resizing your print without changing how far back people will stand leaves the DPI requirement completely unchanged.

Print Width and Print Height instead drive Width (pixels) and Height (pixels) directly: each pixel dimension is simply the corresponding physical dimension in inches multiplied by Required DPI, so a wider or taller print needs proportionally more source pixels at any fixed viewing distance, and Megapixels Needed is just those two pixel counts multiplied together and divided down to millions. Because Required DPI itself depends on Viewing Distance, moving the expected viewing distance also reshapes how many pixels the same physical print size will require -- a poster meant to be viewed up close needs far more source resolution than the identical poster meant to be viewed from across a room. As a practical reference point, most commercial presses and photo labs don't resolve meaningfully beyond about 300 DPI even up close, so Required DPI figures well above that (very short viewing distances) mostly indicate diminishing returns rather than a hard file requirement.