Build a comparison from a URL

Every saved comparison on this site has its own address. You can also go the other way round and write the address yourself. Put the objects in the query string and the page draws them. No key is needed and there is no request to make first. When every object resolves, the visit also gives the comparison a permanent /comparison/… page, linked under the viewer; the same objects always lead to the same page, whatever order they are written in.

https://comparesizes.com/compare?item=Name:LxWxHunit&item=Name:LxWxHunit

Examples

Parameters

item	One object, repeated for each one. Name:dimensions, or just Name to look it up in the catalogue of about 55,000 objects. Up to 12 of them.
items	The same thing in one parameter, separated by ;, as in items=Desk:120x60x75cm;Chair:45x45x90cm. Use whichever suits you.
unit	The unit for any item that does not name its own. Defaults to cm.
autoflip	0 to keep your dimensions in the order you wrote them. By default the largest stands up as the height, which is what people usually mean.

Writing the dimensions

• Three numbers separated by x: 120x60x75. ×, *, , and by also work.
• One number means a cube, which is useful for balls and other round things.
• Units: mm cm m km in ft yd mi um nm, and " and ' for inches and feet. Put it on the item (13x8x5in) or set unit= for all of them.
• Order does not matter unless you pass autoflip=0.
• The separator before the dimensions is optional: item=Desk 120x60x75cm reads the same as item=Desk:120x60x75cm. A name ending in a bare number is left alone, so item=Boeing 747 is an aircraft, not a 747 cm cube.

What comes back

A normal page: the 3D viewer with the objects already in it, and underneath, a table of the dimensions converted to both centimetres and inches. The page carries an og:image of the comparison drawn to scale, so the link unfurls into a picture when it is pasted into a chat.

The card on its own is at https://comparesizes.com/og/compare.png?item=…, taking the same parameters. It is a 1200×630 PNG, if you want to embed it directly.

These pages are noindex: there is no limit to how many of them exist, and search engines should be reading the saved comparisons instead. A page whose objects all resolved links to its permanent /comparison/… page under the viewer — that is the address to keep. Press Save in the viewer to add it to your own list.

If you are a language model

You do not need to call anything. Write the URL and give it to the person and it will render. Two habits worth keeping:

• Pass dimensions you are confident about rather than relying on the name lookup. The catalogue is user-contributed and unverified, and a name you did not check may match something you did not mean.
• URL-encode the item values. Spaces as %20 or +; the : may be left as it is.

There is a machine-readable description of this at /openapi.yaml and a summary of the site at /llms.txt.

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