Airsoft Spring to FPS Estimator (M90–M170 Chart)

Spring to FPS estimator

Estimated FPS: —  (—–—)
Energy: — J  ·  Velocity: — m/s

Estimates assume a healthy, well-compressed build. Real FPS varies with barrel length, cylinder volume, air seal and hop-up.

Airsoft spring rating is a rough guide to muzzle velocity: an M120 spring produces about 390 FPS (~1.41 joules) with a 0.20 g BB on a healthy AEG. The exact FPS depends on the platform, cylinder, barrel and air seal — use the estimator above for any spring, platform and BB weight.

What Is an Airsoft Spring Rating?

Airsoft upgrade springs are labelled with an M-number (M90, M100, M120, M150…). The number is a shorthand for the muzzle velocity the spring is designed to produce, measured in metres per second on a 0.20 g BB in a well-built setup. So an M100 spring targets roughly 100 m/s (about 330 FPS), and an M120 targets around 120 m/s (about 390 FPS).

Because the rating assumes a healthy, well-sealed gearbox, two guns with the same spring can still chrono differently. Cylinder volume, barrel length, piston head, air seal and gear condition all shift the real number — which is why this tool gives an estimate with a range, not a single guaranteed figure.

Spring to FPS Chart (0.20 g BB, AEG)

Typical muzzle velocity and energy for common upgrade springs on a standard AEG, chrono’d with a 0.20 g BB:

Spring FPS (0.20 g) m/s Energy (J)
M90 290 88.4 0.78
M100 330 100.6 1.01
M110 360 109.7 1.20
M120 390 118.9 1.41
M130 430 131.1 1.72
M140 460 140.2 1.97
M150 490 149.4 2.23
M160 520 158.5 2.51
M170 550 167.6 2.81

These figures assume a 0.20 g BB. Heavier BBs lower the FPS while keeping roughly the same energy — see below.

AEG vs Spring Sniper

A bolt-action spring sniper (VSR-style) uses a full cylinder and usually a longer, tighter barrel, so it extracts a little more velocity from the same spring than a short-stroked AEG. As a rule of thumb a sniper build runs around 5% higher than the AEG figure for the same spring — an M120 that gives ~390 FPS in an AEG can reach ~410 FPS in a well-built VSR. The estimator lets you switch between the two platforms.

How BB Weight Changes the Result

A spring delivers a fixed amount of energy. Put that energy behind a heavier BB and it leaves the barrel slower, so FPS drops as BB weight rises even though the joules stay almost the same. For example, an M120 build that chronos 390 FPS on a 0.20 g BB drops to roughly 318 FPS on a 0.30 g BB. This is why fields that set a joule limit let you run heavier ammo without losing energy headroom.

Why Spring FPS Is Only an Estimate

Real chrono numbers depend on more than the spring:

  • Air seal — a leaking cylinder or nozzle loses FPS fast.
  • Cylinder volume vs barrel length — a mismatched cylinder under- or over-volumes the barrel.
  • Piston and spring guide — worn parts and friction sap energy.
  • Break-in — new springs often settle 5–10 FPS after a few hundred rounds.

Always chrono your gun before a game rather than trusting the spring label alone.

How to Use This Spring Estimator

  1. Pick your spring rating (M90–M170).
  2. Choose the platform — AEG or spring sniper.
  3. Select the BB weight you will chrono with.
  4. Read the estimated FPS (with a realistic range), energy in joules and velocity in m/s.

Frequently Asked Questions

What FPS is an M100 spring?
An M100 spring produces roughly 330 FPS (about 100 m/s, ~1.0 joule) on a 0.20 g BB in a healthy AEG.
What FPS is an M120 spring?
An M120 spring gives around 390 FPS (about 120 m/s, ~1.4 joules) on a 0.20 g BB. A full-cylinder sniper build can reach ~410 FPS.
What FPS is an M90 spring?
An M90 spring is around 290 FPS (~0.78 joules) on a 0.20 g BB, making it a common choice for CQB-legal builds.
Does BB weight change spring FPS?
Yes. Heavier BBs leave the barrel slower for the same spring energy, so FPS drops as BB weight rises while joules stay about the same.
Is the spring rating exact?
No. The M-number is a target velocity that assumes a healthy, well-sealed build. Air seal, cylinder volume, barrel and wear all shift the real chrono reading, so treat it as an estimate.
What spring do I need for 350 FPS?
Roughly an M105 spring on a standard AEG with a 0.20 g BB. Always chrono and adjust, as builds vary.

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