Units & Measures
From the cubit to the Planck constant — how humans learned to agree on length, mass, time, and temperature. Explore 43 units across five millennia, trace the great redefinitions, and convert between any pair.
Gallery
43 units spanning five thousand years — from the Egyptian cubit to the Planck-constant kilogram. Click any card to copy its description.
No units in this category.
Timeline
Key milestones from 2700 BC to 2019 — scroll to trace how measurement went from pharaoh's arm to fundamental constants.
Playground
Hands-on tools for converting units, exploring historical measures, and understanding the seven SI base units.
Enter a modern measurement and see how many historical units it equals — or flip direction to convert an ancient unit into metric.
The seven base units that all others derive from. Since the 2019 redefinition, each is fixed by a physical constant — no artifacts, no drift.