Know the physical size before another app guesses.

viewBox and physical size solve different problems.

The viewBox describes the internal coordinate system of an SVG. The root width and height describe how large that coordinate system should be displayed. A file can therefore have perfectly valid geometry and still arrive at the wrong physical size when another application interprets unitless or pixel dimensions differently.

Explicit millimetres or inches give the strongest physical-size signal. Pixel and unitless dimensions can still be converted using the CSS reference of 96 px per inch, but that is an interpretation rather than a manufacturing guarantee. This checker shows that distinction instead of silently treating every number as millimetres.

Check dimensions before you change geometry.

Use this tool when an SVG imports too large or too small, when a file has a viewBox but no obvious physical units, or when you need to hand a file to another application at a known size. The export option changes only the root width and height attributes; it leaves path data, transforms and the viewBox untouched.

If the problem is open geometry, duplicate cut lines or other fabrication-file structure, use Open Path & Gap Checker, Duplicate Cut Line Finder or the broader Fabrication Doctor.

Boundary: a correctly sized SVG can still fail for material, machine, kerf or geometry reasons. Always verify the final job in the actual downstream software.