Design AtlasErgonomics doesn't start from a hunch about what feels comfortable — it starts from measured anthropometric data. Even picking a single handle diameter means checking the range between the 5th percentile (smaller hands) and 95th percentile (larger hands) of adult hand circumference, and landing somewhere both a small hand can close around and a large hand won't find cramped. Most consumer products are designed to satisfy that 5th-to-95th-percentile band, not everyone — covering 100% of hand sizes gets exponentially more expensive.
Anything touched repeatedly — a handle, a button — has to account for grip force and repetitive strain, not just size. A handle that's held with the wrist bent is fine for a moment but raises carpal tunnel risk with repeated use, so the grip gets placed where the wrist can stay in its natural, neutral angle. Furniture height and a desk's reach envelope (how far an arm can comfortably extend) are sized the same way.
A UI's minimum touch-target size — roughly 44px, the smallest a thumb can reliably tap — is the same idea moved onto a screen: a physical finger's width and precision set the floor for how small an on-screen button can be. It's ergonomics' digital cousin.
When to use
When designing a grip, handle, button, or workspace that a hand or arm touches directly, or checking whether repeated use causes strain.