Airsoft Calculators: FPS to Joules, RPS, BB Weight & HPA

Airsoft Calculators

Free airsoft calculators: FPS to joules, spring and BB weight, rate of fire (RPS), cylinder to barrel volume, and HPA shots per tank.

Last updated Nov 6, 2026

Work out your airsoft gun's power, rate of fire and air use in seconds. Each calculator is free, works on your phone, and explains what it's doing.

FPS to Joules Calculator: turn your chrono reading in FPS and your BB weight into joules (and back), to check your gun against a field's limit.
Spring, Barrel & BB to Velocity & Joules Calculator: estimate the FPS and joules a spring, barrel and BB weight will give before you open your gearbox.
BB Weight Optimization Calculator: find the BB weight that suits your gun's power, for range and accuracy.
Rounds per Second (RPS) Calculator: estimate your rate of fire from your motor, gears and battery, or your HPA engine.
Cylinder to Barrel Volume Efficiency Calculator: match your cylinder to your barrel length for consistent FPS.
HPA Tank Size Number of Shots Estimator: estimate how many shots you'll get from a fill of your HPA tank.

The results are estimates: always chrono your gun at the field with the BBs you'll use.

Work out your airsoft gun's power, rate of fire and air use in seconds. Each calculator is free, works on your phone, and explains what it's doing.

FPS to Joules Calculator: turn your chrono reading in FPS and your BB weight into joules (and back), to check your gun against a field's limit.
Spring, Barrel & BB to Velocity & Joules Calculator: estimate the FPS and joules a spring, barrel and BB weight will give before you open your gearbox.
BB Weight Optimization Calculator: find the BB weight that suits your gun's power, for range and accuracy.
Rounds per Second (RPS) Calculator: estimate your rate of fire from your motor, gears and battery, or your HPA engine.
Cylinder to Barrel Volume Efficiency Calculator: match your cylinder to your barrel length for consistent FPS.
HPA Tank Size Number of Shots Estimator: estimate how many shots you'll get from a fill of your HPA tank.

The results are estimates: always chrono your gun at the field with the BBs you'll use.

Common questions

›How do I convert FPS to joules?

Energy in joules is half the BB's mass in kilograms times its speed in metres per second, squared. For example, a 0.20 g BB at 400 FPS (about 122 m/s) carries about 1.49 joules. The FPS to Joules Calculator does it for any BB weight.

›Why do fields talk about joules and not only FPS?

FPS changes with the BB: a heavier BB leaves the barrel slower, so the same gun reads lower in FPS with heavier BBs. Joules take the BB's weight into account, so many fields set limits in joules, or say which BB weight to chrono with.

›What FPS or joule limit will a field ask for?

Each field and event sets its own limits, often different for rifles, DMRs and snipers, with minimum engagement distances for the more powerful ones. Check the field's or event's rules before you play: they're on its page in the Directory or Events.

›Are the results exact?

They're estimates. Air seal, hop-up, barrel and BB quality all change the real numbers, so chrono your gun with the BBs you'll use before you play.

›Which BB weight should I use?

It depends on your gun's power and how you play: heavier BBs hold their line better at range but need more power to carry. The BB Weight Optimization Calculator suggests a weight for your gun.

›How many shots will I get from my HPA tank?

It depends on the tank's size and fill pressure, the output pressure you run, and how much air your gun uses each shot. The HPA Tank Size Number of Shots Estimator works it out from those.

Airsoft Calculators

Common questions

In this guide