How big can I print my image?

Summary

How big can I print my image? Jul 24, 2025 (Photography) For an image to look as sharp as real life, it needs to have a resolution higher then that of the human eye: usually around 1 arcminute, or 1/60th of a degree. $$ \text{Linear resolution} = \frac{\text{Distance}}{\text{1 radian}} \times 1 \text{ arcminutes} $$ $$ \text{Linear resolution }(\text{inches}) = \text{Distance (m)} \times 0.0115 $$ $$ \text{Features / Inch } = \frac{87}{\text{Distance (m)}} $$ For an image to look good at 1 meter, around an arms-length, it needs a feature size of 1/87th of an inch. A poster that’s going to be viewed from 2 meters can get away with half that, 1/43th of an inch. Something that’s going to be examined up close, say 50 cm, needs a resolution of 1/172th of an inch. Importantly, the actual resolution of the image is often different from the size of the pixels. If an image looks pixelated when you zoom in, a good rule is to print with a pixels-per-inch of twice the desired resolution: Undersampled image. Small features (stars) take up 2 pixels. Viewing distance PPI 4 meters 43 pixels/inch 2 meters 87 pixels/inch 1 meter 170 pixels/inch 50 cm 350 pixels/inch 25 cm 700 pixels/inch However, if you zoom in and the image looks blurry: Oversampled image. The smallest features still have a lot of pixels. … measure the size of a sharp edge, double it and use that as the conversion factor. Looks like the edges are around 5 pixels, so we have to multiply the desired resolution by 10 to get pixels/inch. If it’s got to look good hanging on a wall (~1 meter), it needs a resolution of 1/87th of an inch: $$ 87 \text{ Inch}^{-1} \times 10 \text{ Pixels} = 870 \text{ PPI} $$ The whole image is 3000x3000 pixels: $$ \frac{3000\text{ Pixels}}{870\text{ PPI}} = 3.4 \text{ Inches}$$ There’s an easy way to test this, just display the image on a screen and zoom in/out until it’s 3.4 inches on both sizes. From closer then 1 meter, some blurriness is visible, but from further some detail is lost. If ...