Pixels to Inches

What this tool is used for

• Working out the physical size an image will print at a given DPI.
• Checking whether an asset has enough pixels for a print at a required size.
• Converting a screen dimension into a physical one for a mockup.
• Sizing an export so a printed piece comes out at the intended dimensions.
• Comparing a screen design's size against a print specification.

Frequently Asked Questions

Why does a pixel have no fixed physical size?

Because it is a device unit, not a length. The same 96px is one inch on a 96 PPI monitor and half an inch on a 192 PPI one. Converting between them requires knowing the display's pixel density, which is why PPI is a required input rather than a constant.

What is the difference between PPI and DPI?

PPI describes a display — pixels per inch of screen. DPI describes a printer — dots of ink per inch. They are used interchangeably and are not the same thing: a 300 DPI print and a 300 PPI screen produce visibly different results because ink dots are not pixels.

Why is 96 the default?

Because CSS defines a reference pixel as 1/96th of an inch, a convention inherited from Windows. It is why 1in in CSS is exactly 96px regardless of the actual monitor — CSS units are a coordinate system, and the browser maps them to hardware pixels afterwards.

Why is 300 the standard for print?

Because the eye stops resolving individual dots at roughly that density at normal reading distance. Below 300 the halftone pattern becomes visible on close inspection; above it the extra data is invisible while the file size keeps growing, so 300 is the practical settling point.

How does a device pixel ratio fit in?

A CSS pixel on a 2× display covers four hardware pixels, so a 100px image renders in the same physical space but needs a 200px source to look sharp. That is what `@2x` assets and `srcset` exist for — the CSS size stays the same and only the source resolution changes.

Common errors and gotchas

• Assuming 72 DPI for print, which is a screen convention and far too low for anything printed.
• Confusing DPI with PPI, and either with the CSS pixel, which is a reference unit rather than a device one.
• Ignoring device pixel ratio, so an image sized in CSS pixels has twice the device pixels.
• Upscaling to reach a print size, which adds pixels without adding detail.
• Reading a screen's reported DPI as its physical one, which the operating system often scales.