FPS to joules calculator
Muzzle energy from velocity and BB weight, checked against Japan’s 0.98 J legal limit and common field limits.
0.00J
- Japan (18+) 0.98 J
- Japan (ages 10–17) 0.135 J
- UK (full auto) 1.3 J
- UK (semi / bolt) 2.5 J
- Germany (no F mark) 0.5 J
- France 2 J
The formula
Muzzle energy in joules comes from the BB's mass and velocity:
E (J) = 1/2 × m (kg) × v (m/s)²
Example: a 0.20 g BB at 350 fps is 106.7 m/s, so 0.5 × 0.0002 × 106.7² = 1.14 J. Convert fps to m/s first (1 fps = 0.3048 m/s).
Japan's 0.98 J legal limit
Japan, where airsoft was invented, has one of the strictest limits in the world. The Firearms and Swords Control Law sets a maximum of 3.5 J per cm² of BB cross-section, measured 1 m from the muzzle. A 6 mm BB has a cross-section of about 0.28 cm², which gives the familiar 0.98 J ceiling. Anything above it is classed as a "quasi air gun" and is illegal to own.
On 0.20 g BBs that works out to roughly 99 m/s or 324 fps. Japanese-market guns from Tokyo Marui and others ship well under that, typically 80–95 m/s. Guns for ages 10–17 are limited to 0.135 J by an industry standard.
If you're bringing a gun to Japan or buying a Japanese-spec gun, the 0.98 J limit is why Japanese guns feel underpowered compared with US or European builds, and why many fields in Japan chrono on 0.20 g with hop applied.
Field limits elsewhere
| Country | Limit | Notes |
|---|---|---|
| Japan | 0.98 J | Legal limit, 6 mm BBs. 8 mm BBs have a higher value because of the larger cross-section |
| United Kingdom | 1.3 J full auto / 2.5 J semi or bolt | Defined by the Policing and Crime Act 2017 |
| Germany | 0.5 J without F mark / 7.5 J with F mark, 18+ | Fields usually set lower limits |
| France | Under 2 J | Free sale to adults; 2 J and above is regulated |
| United States | No federal limit | Fields commonly cap AEGs around 1.1–1.5 J, DMRs and sniper rifles higher with minimum engagement distances |
Laws change. Check the current rules before you travel or import.