FPS → Energy
Velocity: — m/s · — mph
Energy → FPS
What Is FPS in Airsoft?
FPS stands for feet per second and refers to the speed at which a BB leaves the barrel of an airsoft gun. It is one of the most common measurements players use to compare replicas, check field limits, and chrono their guns before a game.
If an airsoft rifle shoots at 350 FPS, the BB travels roughly 350 feet in one second under ideal conditions. While FPS is useful for comparing velocity, it does not tell the full story about the actual energy of the BB — which is why many fields now focus on joules rather than FPS. Two guns can show the same FPS but produce different energy depending on the BB weight.
What Are Joules in Airsoft?
A joule is a unit of energy. In airsoft, joules measure the actual kinetic energy of the BB as it leaves the barrel. Unlike FPS, which only measures speed, joules account for both velocity and BB weight, giving a more accurate picture of how powerful a gun really is. Most modern fields use joule limits because they keep safety standards consistent regardless of BB weight.
- 350 FPS with a 0.20 g BB ≈ 1.14 joules
- The same FPS with a heavier BB gives a different energy reading
- Same FPS does not always mean the same power
Why BB Weight Matters
A common misconception is that FPS alone determines how powerful an airsoft gun is. In reality, BB weight plays a major role. Heavier BBs carry energy differently and retain momentum better over distance, which is why fields require a specific chrono weight or use joule limits instead of raw FPS.
| BB Weight | Typical Use |
|---|---|
| 0.20 g | Standard chrono testing |
| 0.25 g | General outdoor play |
| 0.28 g | Improved stability and accuracy |
| 0.30 g+ | DMR and long-range setups |
| 0.36 g+ | High-performance rifles |
If you switch from 0.20 g to 0.30 g BBs, FPS usually drops, but the actual energy can stay similar or even rise on some platforms.
Common FPS to Joule Conversions
The most frequently searched airsoft FPS conversions, using 0.20 g BBs:
| FPS | Joules (0.20 g) |
|---|---|
| 300 FPS | 0.84 J |
| 328 FPS | 1.00 J |
| 350 FPS | 1.14 J |
| 375 FPS | 1.31 J |
| 400 FPS | 1.49 J |
| 425 FPS | 1.68 J |
| 450 FPS | 1.88 J |
| 475 FPS | 2.10 J |
| 500 FPS | 2.32 J |
If your exact FPS is not listed, use the calculator at the top of this page for an instant conversion.
What Is Joule Creep?
Joule creep is when an airsoft gun produces higher muzzle energy with heavier BBs than its standard chrono reading suggests. It is most common in HPA systems and heavily modified replicas — a gun can chrono within limits on 0.20 g BBs yet exceed the energy cap with heavier ammo. This is exactly why many fields measure energy in joules rather than FPS alone.
Typical Airsoft Energy Limits
Energy limits vary by country, organizer and field. Commonly seen examples:
| Replica Type | Typical Energy Limit |
|---|---|
| CQB Rifle | ~1.0 J |
| Standard AEG | ~1.5 J |
| DMR | ~2.0 J |
| Bolt Action Sniper | ~2.5–3.0 J |
Always verify the exact limits used by your local field before an event.
Joule Limit by BB Weight (Max FPS)
The maximum FPS allowed for a given joule limit, by BB weight. Useful when a field sets a joule cap but you chrono in FPS.
| Joule limit | 0.20 g | 0.25 g | 0.28 g | 0.30 g | 0.32 g |
|---|---|---|---|---|---|
| 1.0 J | 328 FPS | 293 FPS | 277 FPS | 268 FPS | 259 FPS |
| 1.5 J | 402 FPS | 359 FPS | 340 FPS | 328 FPS | 318 FPS |
| 2.0 J | 464 FPS | 415 FPS | 392 FPS | 379 FPS | 367 FPS |
| 2.5 J | 519 FPS | 464 FPS | 438 FPS | 424 FPS | 410 FPS |
| 3.0 J | 568 FPS | 508 FPS | 480 FPS | 464 FPS | 449 FPS |
FPS to Joule Formula
Joules are calculated from BB mass and velocity. FPS is first converted to metres per second, then combined with BB weight in kilograms:
Energy (J) = 0.5 × mass (kg) × velocity² (m/s)
Convert FPS to m/s by multiplying by 0.3048 — or use the FPS to m/s & mph converter for all four units at once. Foot-pounds (ft·lb) = joules × 0.73756.
Airsoft FPS to Joule Chart
Muzzle energy in joules for common BB weights at a given FPS. The lighter the BB, the lower the energy at the same FPS.
| FPS | 0.20 g | 0.25 g | 0.28 g | 0.30 g | 0.32 g | 0.36 g | 0.40 g |
|---|---|---|---|---|---|---|---|
| 200 | 0.37 | 0.46 | 0.52 | 0.56 | 0.59 | 0.67 | 0.74 |
| 225 | 0.47 | 0.59 | 0.66 | 0.71 | 0.75 | 0.85 | 0.94 |
| 250 | 0.58 | 0.73 | 0.81 | 0.87 | 0.93 | 1.05 | 1.16 |
| 275 | 0.70 | 0.88 | 0.98 | 1.05 | 1.12 | 1.26 | 1.41 |
| 300 | 0.84 | 1.05 | 1.17 | 1.25 | 1.34 | 1.51 | 1.67 |
| 325 | 0.98 | 1.23 | 1.37 | 1.47 | 1.57 | 1.77 | 1.96 |
| 350 | 1.14 | 1.42 | 1.59 | 1.71 | 1.82 | 2.05 | 2.28 |
| 375 | 1.31 | 1.63 | 1.83 | 1.96 | 2.09 | 2.35 | 2.61 |
| 400 | 1.49 | 1.86 | 2.08 | 2.23 | 2.38 | 2.68 | 2.97 |
| 425 | 1.68 | 2.10 | 2.35 | 2.52 | 2.68 | 3.02 | 3.36 |
| 450 | 1.88 | 2.35 | 2.63 | 2.82 | 3.01 | 3.39 | 3.76 |
| 475 | 2.10 | 2.62 | 2.93 | 3.14 | 3.35 | 3.77 | 4.19 |
| 500 | 2.32 | 2.90 | 3.25 | 3.48 | 3.72 | 4.18 | 4.65 |
How to Use This FPS to Joule Calculator
- Enter your measured FPS value.
- Select the BB weight used during chrono testing.
- Instantly read the energy in joules and foot-pounds.
- Use the reverse calculator to find the FPS allowed for a specific joule limit.