Dive Math Calculators

Your Surface Air Consumption (SAC) rate is just a personal number: how fast you, specifically, breathe through your tank's air. Some divers sip air, some go through it faster — body size, experience, workload, and how relaxed you are in the water all play a part. A higher number isn't a fitness failing. It's just data about you, and it usually drops as you log more dives and get more comfortable underwater.

It matters because it's the number that turns "how much air is in my tank" into "how long will that actually last me down there." Air use scales with pressure, so you burn through gas faster at 18 m than at 5 m even breathing exactly the same way — your SAC rate is what lets you predict that, before you descend, instead of discovering it from a gauge dropping faster than expected.

Once you have it: divide your usable gas by your SAC rate and the pressure at your planned depth to estimate how many minutes you have. Most divers then build in a real margin — planning to turn the dive and start heading up well before hitting reserve, since exertion, cold, or a shallower-than-average moment can all push your consumption above your calm, resting number.