About the Rounds per Minute Calculator
Rounds per minute (RPM) is the standard way to express how fast a firearm, tool, or repeating mechanism fires or cycles. It is simply a rate: a count of events divided by the time it took, scaled up to a one-minute window so different measurements can be compared on the same basis. This calculator times a short burst — a rounds-fired count over a measured number of seconds — and converts it into RPM, then derives three related figures: the average time between rounds, how long a magazine of a given size lasts at that rate, and a more realistic sustained rate that accounts for reload time.
The core formula
The formula is a simple unit conversion:
- RPM = (rounds fired ÷ time elapsed in seconds) × 60. Multiplying by 60 rescales a per-second rate to a per-minute rate. Firing 10 rounds in 1 second is 10 ÷ 1 × 60 = 600 RPM.
- Time per round (ms) = 60,000 ÷ RPM. This is the average interval between shots, in milliseconds. At 600 RPM, rounds fire on average every 100 ms.
- Time to empty a magazine (seconds) = magazine capacity ÷ RPM × 60. A 30-round magazine at 600 RPM empties in 30 ÷ 600 × 60 = 3 seconds if the trigger is held continuously.
Cyclic rate versus sustained rate
The RPM computed directly from a timed shot count is the cyclic rate of fire — the mechanical speed of the action while the trigger is held with no interruption. In practice, nobody fires that way indefinitely: magazines run empty and must be swapped. The sustained (practical) rate of fire folds reload time into the cycle: sustained RPM = magazine capacity × 60 ÷ (time to empty one magazine + reload time). Because the reload adds dead time with zero rounds fired, sustained RPM is always lower than cyclic RPM, often substantially so for small magazines or slow reloads.
Where these numbers come from and their limits
Manufacturers typically publish a cyclic rate measured under controlled conditions with a fixed ammunition type; a hand-timed burst you measure yourself will vary shot to shot due to timing precision and trigger control, so treat a single measurement as an estimate rather than a certified spec. The sustained-rate figure here assumes exactly one reload pause per magazine and no additional stoppages, aiming pauses, or barrel-cooling breaks — real sustained rates in practice are usually lower once those are added.