In this guide
- What does FPS mean in airsoft?
- Standard UK site FPS limits
- How chrono testing works
- Minimum engagement distances (MEDs)
- The 1.3 joule limit, what about UK law?
- How to set your gun to the right FPS
- Joule creep, what it is and why sites test for it
- Frequently asked questions
- Need help setting your FPS?
FPS limits are one of the first things you’ll encounter when you turn up to play airsoft. Every site in the UK has them, they’re enforced at the start of every game day via chronograph testing and if your gun exceeds the limit, you’re not playing.
But FPS limits aren’t just arbitrary numbers, they exist to keep everyone safe. Understanding how they work, what they mean for your gun and how different roles and platforms are treated will help you prepare properly and avoid the frustration of failing chrono on game day.
This guide covers everything you need to know about airsoft FPS limits in the UK: standard site limits, how chrono testing works, the joules vs FPS debate and how to set your gun up to stay within the rules. If you’re completely new to airsoft, our complete beginner’s guide covers FPS limits as part of the bigger picture.
What does FPS mean in airsoft?
FPS (Feet Per Second) measures the velocity of a BB as it leaves the barrel. A gun shooting 350 FPS means the BB is travelling at 350 feet per second at the muzzle.
Higher FPS doesn’t necessarily mean better, it means the BB has more energy, which increases range slightly but also increases the sting on impact. That’s why sites cap FPS: to keep the game enjoyable and safe for everyone.
FPS vs Joules, what’s the difference?
Joules measure the actual energy the BB carries. This is more accurate than FPS alone because the energy depends on both velocity AND BB weight.
A heavier BB at a lower FPS can carry the same energy (joules) as a lighter BB at a higher FPS. This is why most serious sites now chrono using joules, not just FPS, it prevents players from gaming the system by chronoing with light BBs and then switching to heavy ones (known as “joule creep”).
Quick conversion reference
| FPS (0.20g BB) | Energy (Joules) | Typical Use |
|---|---|---|
| 280 FPS | ~0.84J | CQB / Indoor lower limit |
| 300 FPS | ~0.93J | CQB / Indoor typical limit |
| 328 FPS | ~1.00J | 1 joule limit (some sites) |
| 350 FPS | ~1.14J | Standard AEG limit (most outdoor sites) |
| 400 FPS | ~1.49J | DMR limit (some sites) |
| 450 FPS | ~1.88J | DMR / Support gun limit |
| 500 FPS | ~2.32J | Bolt action sniper limit |
Standard UK site FPS limits
There’s no single “UK legal limit” for airsoft FPS, each site sets its own rules. However, most sites follow broadly similar guidelines. Here are the typical limits you’ll encounter:
Outdoor / Woodland sites
| Role / Weapon Class | Typical FPS Limit (0.20g) | Joule Limit | Minimum Engagement Distance |
|---|---|---|---|
| AEG / Assault Rifle | 350 FPS | 1.14J | None or 10m |
| Pistol / SMG | 350 FPS | 1.14J | None |
| DMR (Semi-auto locked) | 400-450 FPS | 1.49-1.88J | 20-30m |
| Support Gun / LMG | 350-400 FPS | 1.14-1.49J | Varies |
| Bolt Action Sniper | 450-500 FPS | 1.88-2.32J | 30m+ |
CQB / Indoor sites
| Weapon Type | Typical FPS Limit (0.20g) | Joule Limit | Engagement Distance |
|---|---|---|---|
| All weapons | 280-350 FPS | 0.84-1.14J | Bang rule at close range |
| Pistols only (some sites) | 280-300 FPS | 0.84-0.93J | None |
Always check your site’s specific rules before game day. Limits vary between sites and some sites use joule-based chrono while others use FPS with a specific BB weight. If you play at sites in Kent, check our Kent airsoft sites guide for details on local venues.
How chrono testing works
At the start of every game day, every player’s guns are tested on a chronograph (“chrono”). This is a device that measures the velocity of a BB as it passes through two sensors a fixed distance apart.
What to expect
- Queue up at the chrono station, this is usually one of the first things you do on arrival
- The marshal will provide BBs, most sites supply standard 0.20g BBs for chrono testing to ensure consistency
- Fire 3-5 shots through the chrono, the marshal checks for consistency and maximum velocity
- Pass or fail, if you’re within limits, you get a wristband or tag. If you fail, you need to address the issue
What happens if you fail chrono?
Don’t panic. Options typically include:
- Swap your spring, if your gun has a quick-change spring system, you can fit a lighter spring on site
- Use a different gun, if you brought a backup
- Rent a site gun, most sites offer rentals
- Sit out, worst case scenario
Consistent failure usually means your spring is too strong for the site’s limits. A spring swap is a quick fix, read our upgrade guide for details on spring ratings or bring your gun to our Rochester workshop and we’ll set it to your preferred FPS.
Minimum engagement distances (MEDs)
Higher FPS comes with restrictions. If your gun shoots above the standard AEG limit, you’ll have a minimum engagement distance (MED), the closest range at which you can shoot another player.
MEDs exist because a BB hitting someone at point-blank range from a 500 FPS sniper rifle is significantly more painful (and potentially dangerous) than one from a 350 FPS AEG.
Typical MEDs
- Up to 350 FPS / 1.14J: No MED (or bang rule only)
- 350-400 FPS / 1.14-1.49J: 15-20m MED
- 400-450 FPS / 1.49-1.88J: 20-30m MED
- 450-500 FPS / 1.88-2.32J: 30m+ MED
If an enemy gets inside your MED, you cannot shoot them. Most sites require you to call “bang” or “surrender” instead. This is why snipers and DMR players often carry a sidearm (pistol) for close encounters.
Free tool: work out your muzzle energy
Not sure what your gun puts out in joules? Try our free Airsoft FPS and Joule Calculator to convert FPS to joules on any BB weight, check the 1.3 J and 2.5 J legal limits, and see how your FPS changes across BB weights.
The 1.3 joule limit, what about UK law?
You’ll sometimes hear that airsoft guns must be below 1.3 joules or they become “firearms” under UK law. This is a simplification, here’s the actual position:
- Under the Firearms Act 1968, an air weapon that exceeds 1.3 joules (approximately 370 FPS with 0.20g) is classified as a firearm and requires a firearms certificate
- However, this applies to lethal barrelled weapons, airsoft guns are generally not considered capable of causing lethal injury so in practice, the 1.3J threshold is interpreted differently for airsoft
- The practical legal grey area sits between 1.3J and 2.5J. Most sites set their upper limit (bolt action snipers) at around 2.3J / 500 FPS to stay well within safe and legal territory
- Above 2.5 joules is unambiguously into air weapon territory and would require licensing
For practical purposes: If your gun is set within your site’s chrono limits, you have nothing to worry about. Sites set their limits well within safe and legal bounds.
For a broader overview of UK airsoft legislation including the VCRA, read our full UK airsoft rules guide.
How to set your gun to the right FPS
Your gun’s FPS is primarily determined by the spring inside the gearbox. A stronger spring = higher FPS. Here’s a rough guide to spring ratings:
| Spring Rating | Approximate FPS (0.20g) | Best For |
|---|---|---|
| M90 | ~280-300 FPS | CQB builds |
| M100 | ~320-340 FPS | Standard outdoor AEG |
| M110 | ~340-360 FPS | Standard outdoor AEG (upper range) |
| M120 | ~370-400 FPS | DMR builds |
| M130 | ~400-420 FPS | DMR builds |
| M140 | ~420-450 FPS | High-power DMR / Sniper |
| M150-M170 | ~450-500+ FPS | Bolt action sniper |
Spring ratings are approximate, actual FPS depends on air seal quality, barrel length, cylinder volume and temperature. Always chrono your gun after a spring change.
If you play at multiple sites with different limits, a quick-change spring system lets you swap springs in seconds without opening the gearbox. Check our upgrade guide for more on springs and gearbox tuning.
Joule creep, what it is and why sites test for it
Joule creep occurs when a gun’s energy output increases with heavier BBs, the opposite of what simple physics would predict. This happens because of how gas guns and some AEGs with long barrels handle heavier BBs: the BB stays in the barrel longer, receiving more energy from the expanding gas or air.
This is why many sites now chrono with the BB weight you’ll actually be using or test in joules rather than FPS. If you chrono at 350 FPS with 0.20g BBs but then switch to 0.30g BBs, your energy output could actually be higher, meaning you’re effectively exceeding the site’s energy limit.
How to avoid issues: Chrono with the BBs you’ll actually use in-game. Be honest with marshals about what weight you’re running. If your site chronos with 0.20g BBs only, make sure your gun isn’t prone to joule creep (mainly a concern with GBB rifles and HPA systems).
Frequently asked questions
What is the legal FPS limit for airsoft in the UK?
There’s no single UK legal FPS limit for airsoft. Each site sets its own limits. Typical outdoor limits are 350 FPS for AEGs, 450 FPS for DMRs and 500 FPS for bolt action snipers (all measured with 0.20g BBs). The important thing is to stay within your site’s specific rules.
Can I play airsoft with a gun over 350 FPS?
Yes, if it’s a DMR or sniper platform and the site allows it. Higher FPS classes come with minimum engagement distances and usually require the gun to be locked to semi-auto (DMRs) or bolt action only. Check your site’s rules for their specific class limits.
Do all sites have the same FPS limits?
No. While most outdoor sites use similar guidelines (around 350 FPS for AEGs), limits can vary. CQB sites are typically lower (280-350 FPS). Some sites are stricter than others. Always check before you go.
What if my gun is just over the limit?
Most sites have a small tolerance (usually 5 FPS) but don’t rely on this. If you’re chronoing at 348-352 FPS against a 350 FPS limit, a spring change to something slightly lighter will give you a consistent safety margin. Better to be comfortably under than right on the edge.
Does temperature affect FPS?
Yes, especially for gas-powered guns. Gas expands more in warm weather and less in cold weather so a GBB pistol shooting 330 FPS in summer might only manage 290 FPS on a cold winter morning. AEGs are less affected but can still show slight variation.
Need help setting your FPS?
If you need a spring change, FPS tuning or want your gun set up for a specific site’s limits, our in-house workshop can sort it out. We’ll chronograph your gun, fit the right spring and make sure it’s shooting consistently at the FPS you want.
Browse our springs if you prefer to do it yourself or read our maintenance guide for tips on keeping your gun performing reliably.
Visit us: A10 Spectrum Business Centre, Medway City Estate, Rochester, Kent ME2 4NP
Email: [email protected]
