Band Resistance Calculator
Bands stack. Put two on the same anchor and their tensions add up, which is how a handful of bands covers a range no single band could. Edit the list to match the set you actually own.
Tensions add, but only at the same stretch.
Two bands anchored side by side and pulled to the same length share the load, so the resistance you feel is the sum of what each band produces at that length. That is the whole arithmetic here: the minimums add, and the maximums add.
The caveat is the one that catches people out. A flat band's tension depends on how far it is stretched, and the number printed on the packet is measured at one particular stretch that the manufacturer picked. Stack a short band with a long one and they will not be at the same percentage of their length, so the real total lands somewhere inside the range rather than at the top of it. Bands of the same length stack predictably; mismatched lengths do not.
Tube bands with handles usually carry a single rating rather than a range. Leave the second box empty for those and the calculator treats the band as flat at that number.
The Rubber Bands app does this for you while you train: turn on band stacking in your gym profile and the band picker keeps a running total for each set, then uses it to work out when you have earned more resistance.
Numbers are the easy part.
Rubber Bands turns a goal into a schedule you can actually keep, built around the resistance bands you already own.