SAC Rate (Surface Air Consumption)

A diver's breathing gas consumption normalized to surface pressure, typically 15 to 25 L/min for relaxed divers, used to plan gas needs for any depth.

SAC rate, surface air consumption, is how much gas you breathe per minute expressed at surface pressure, so it can be scaled to any depth. Because ambient pressure doubles at 10 m, a diver who uses 20 liters per minute at the surface uses 40 at 10 m and 60 at 20 m. Knowing your SAC turns gas planning from guesswork into arithmetic: multiply SAC by planned pressure in atmospheres and by time, and you know the volume a dive segment will cost.

You calculate it from any logged dive: gas used, converted to liters via cylinder size, divided by dive time and by the average absolute pressure of the dive. Relaxed experienced divers typically land between 15 and 25 L/min, with stress, cold, poor trim, and finning against current all pushing the number up. The related term RMV, respiratory minute volume, is often used interchangeably, though some divers reserve SAC for pressure based figures in bar or psi per minute.

A dive log that stores start and end pressures alongside depth and time computes this automatically, and watching your SAC fall over a season is one of the most satisfying trends a logbook can show. Compare like with like, though: a drift dive in a 3 mm suit and a cold quarry dive in a drysuit are different animals, so track your rate per conditions rather than as a single number.