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Free Ruler vs Length: catalog facts
Free Ruler	Length
Free Free and open source, with optional donations.	Free Free and open source under the GPL-3.0-or-later licence.
macOS	Linux
Measures in pixels, millimeters or inches Single-key shortcuts for every main action	Measures anything visible on screen Supports several units, including pixels and centimetres
macOS only Requires macOS Sonoma or later; older builds are on the releases page	Linux only Small project with few contributors
Downloadable app	Downloadable app
Open source	Open source
License not stated	License: GPL-3.0-or-later
No account needed	No account needed
Works offline	Works offline
Official website Full listing and sources Checked October 1, 2026	Official website Full listing and sources Checked October 1, 2026

Catalog facts only. Anything “not stated” is unconfirmed. Check full listings for details.