Resistance band standard (F₁₀₀)

How Calistree rates and compares resistance bands

Every band's rating is its F₁₀₀: the force it pulls with at 100% elongation - when its stretched length is exactly twice its resting (unstretched) length. This single value is what Calistree uses to compare bands, decide which is harder, and track your progress: less force is harder for assistance, more force is harder for resistance.

Manufacturers often quote a different elongation. If you only have a force at, say, 150% elongation, Calistree can estimate F₁₀₀ for you:

F₁₀₀ ≈ Fₑ × 100 / e

This is an estimate only - real bands aren't perfectly linear, so a rating measured at a different elongation, or a manufacturer's stated range, is only approximate. You can always type the number in directly instead, or edit the calculated estimate before saving.