Airsoft BBs: which weight to use (0.20, 0.25, 0.28…) and what changes
BB weight changes velocity, trajectory and wind resistance. Here's how many FPS a gun makes with different weights and how to choose, starting from one fact: at the same energy a heavier BB is slower.
Updated 2026-11-08 · 2896 replicas in the database
Why velocity is measured with 0.20 g
Manufacturers and shops quote FPS with 0.20 g BBs, the standard weight. That's why AirsoftDex computes joules with 0.20 g when the source doesn't state the weight, and marks them as "estimated". The formula is E = ½ · m · v².
Same gun, different BBs
Approximate velocity (FPS) with different weights, starting from FPS measured with 0.20 g and assuming energy stays the same. In practice heavier BBs often keep similar energy or gain a little.
| With 0.20 g | Joules | 0.20 g | 0.25 g | 0.28 g | 0.30 g | 0.32 g | 0.36 g |
|---|---|---|---|---|---|---|---|
| 300 FPS | 0.84 | 300 | 268 | 254 | 245 | 237 | 224 |
| 328 FPS | 1.00 | 328 | 293 | 277 | 268 | 259 | 244 |
| 350 FPS | 1.14 | 350 | 313 | 296 | 286 | 277 | 261 |
| 380 FPS | 1.34 | 380 | 340 | 321 | 310 | 300 | 283 |
The 1 joule limit for each weight
| BB weight | FPS at 1 J | m/s at 1 J |
|---|---|---|
| 0.12 g | 424 | 129.1 |
| 0.20 g | 328 | 100.0 |
| 0.23 g | 306 | 93.3 |
| 0.25 g | 293 | 89.4 |
| 0.28 g | 277 | 84.5 |
| 0.30 g | 268 | 81.6 |
| 0.32 g | 259 | 79.1 |
| 0.36 g | 245 | 74.5 |
| 0.40 g | 232 | 70.7 |
| 0.43 g | 224 | 68.2 |
| 0.45 g | 219 | 66.7 |
Details and legal references in the 1 joule limit guide.
Which weight to choose
- 0.20 g: the reference weight; fine for pistols and low-power guns, but drifts in wind.
- 0.25 g: the most common choice for AEGs under 1 J: steadier flight without losing too much speed.
- 0.28–0.30 g: for long-barrel guns with a well tuned hop-up; better accuracy at medium range.
- 0.32 g and up: typical of sniper rifles tuned to the limit; need hop-ups suited to heavy BBs.
When you change weight re-adjust the hop-up: a heavier BB needs more spin to fly straight.
Quality and biodegradable BBs
BBs with consistent weight and diameter, smooth surface and no seams make the gun more accurate and protect the barrel and bucking. Many fields require biodegradable BBs: check the rules before playing.
FAQ
Which BB weight for an AEG under 1 joule?
Many players use 0.25 g as a balance of stability and range; 0.28–0.30 g on long-barrel guns with a well tuned hop-up. 0.20 g is the standard weight used to measure velocity.
Do heavier BBs push me over the limit?
Energy usually stays about the same, sometimes slightly higher: that's why fields often chrono with the weight you actually use. Chrono your gun with your BBs.
Are biodegradable BBs mandatory?
Not by law everywhere, but many fields require them. Check the field rules before playing.
Why are cheap BBs a problem?
Uneven weight and diameter, seams and rough surfaces hurt accuracy and can damage the barrel and hop-up bucking.
More guides
First airsoft gunPower systemsBatteriesHop-upChronographAEG maintenanceTransportHop-up buckings1 J limitJ/FPS converter