Airsoft: A Comprehensive Guide to FPS and Joules

Airsoft is a great hobby that simulates firearm combat using replica firearms that shoot plastic BBs. As a beginner or even as an experienced player, it’s essential to understand the critical elements that define the game, such as FPS and Joules.

FPS stands for Feet Per Second and is a measure of the speed at which a BB travels while Joules are the units used to measure the kinetic energy of the BB. In general, the higher the FPS, the faster the BB is moving toward the target. The higher the Joules the harder it will impact the target.

Joules Calculator
Mass (g)

This comprehensive guide will provide an in-depth look at these concepts, their significance in Airsoft, and their practical applications.

Relationship Between FPS and Joules

FPS and Joules are closely related, as they both contribute to an airsoft gun’s overall performance. The kinetic energy (Joules) of a BB is directly proportional to its speed (FPS) and mass. This means that while a heavier BB may have a lower FPS, its kinetic energy remains constant, ensuring consistent performance and impact force on the target.

It’s essential to understand that while FPS and Joules are related, they measure different aspects of an airsoft gun’s performance. FPS measures the BB’s velocity, while Joules measure its kinetic energy.

Both parameters must be considered when evaluating an airsoft gun’s performance, power, and consistency.

FPS: Defining Velocity in Airsoft

FPS stands for Feet Per Second and is a measure of the speed at which a BB exits the barrel of an airsoft gun. It is the primary parameter used to gauge an airsoft gun’s performance, as it provides an idea of how fast and far a BB can travel in the air. The higher the FPS, the faster the BB moves through the air, resulting in increased range and potential impact force on the target.

Joules: Measuring Kinetic Energy and Power

While FPS is an essential factor, it doesn’t provide a complete picture of an airsoft gun’s performance. This is where Joules come into play. Joules are the units used to measure the kinetic energy of a projectile, in this case, the BB. Kinetic energy is a crucial parameter, as it determines the amount of energy transferred to the target upon impact. The higher the Joules, the more powerful the airsoft gun.

The formula for calculating joules is:
Joules = (FPS/3.2808399)^2 ∗ 0.5 ∗ mass/1000

Factors Affecting FPS and Joules

Several factors can influence FPS and Joules, including the airsoft gun’s internal components and the weight of the BB. Elements such as the barrel length, hop-up system, and compression components play a significant role in determining the gun’s FPS and Joules.

Additionally, the weight of the BB can affect the projectile’s velocity, with heavier BBs typically resulting in lower FPS but consistent kinetic energy.

Joule Creep: An Exception to the Rule

Joule creep is a phenomenon that occurs when an airsoft gun’s kinetic energy increases without a corresponding increase in FPS. This can happen when there is an excess or shortage of air in the barrel at the time of firing, leading to an imbalance in the BB’s acceleration and resulting in inconsistent performance and accuracy.

Joule creep is more commonly observed in High-Pressure Air (HPA) systems and Gas Blowback Rifles (GBBRs) than in Automatic Electric Guns (AEGs). Players must be aware of this phenomenon and take necessary precautions to ensure that their airsoft guns remain within legal limits and maintain consistent performance during gameplay.

Why Regulate FPS and Joules in Airsoft?

Regulating FPS (Feet Per Second) and Joules in airsoft is important for safety reasons and to ensure a fair and balanced gameplay experience. Here are the key reasons for regulating FPS and Joules in airsoft:

Player Protection: Regulating FPS and Joules helps protect players from excessive pain or discomfort. Higher velocities can lead to increased pain upon impact, potentially discouraging players from participating or causing unnecessary discomfort during gameplay.

Safety: Regulating the FPS and Joules helps prevent injuries and ensures the game is safe for participants. If the velocity of BBs is too high, it increases the risk of causing harm to players, particularly if shots hit sensitive areas such as the face. By implementing limits, the risk of serious injuries is reduced.

Field and Venue Regulations: Many airsoft fields and venues have specific rules and regulations in place regarding FPS and Joules limits. These limits are established to comply with local laws, insurance requirements, and safety standards. Adhering to these regulations allows airsoft games to be conducted in a controlled and safe environment.

Fairness and Balance: Consistent FPS and Joules limits ensure fairness and balance among players. When everyone is playing within the same limits, it creates a level playing field where skill, tactics, and teamwork become the determining factors in the game’s outcome. Limiting the velocity prevents some players from gaining an unfair advantage due to overpowered guns.

Equipment Consistency: Regulating FPS and Joules helps maintain consistency in equipment performance. By setting limits, it ensures that airsoft guns are within a reasonable range and prevents the use of heavily modified or unsafe weapons that could compromise the integrity of the game.

Compliance with Airsoft Organizations: Various airsoft organizations and associations have established guidelines and standards for FPS and Joules limits. These organizations promote safety, fair play, and consistency across different airsoft communities. Adhering to their guidelines helps maintain a unified approach to safety and gameplay standards.

It is crucial for players, event organizers, and field operators to be aware of and comply with the specific FPS and Joules limits set by their local regulations, field rules, or airsoft organizations. This ensures the safety and enjoyment of all participants while promoting a positive and responsible airsoft community.

Playing Airsoft Safely and Legally

Understanding the concepts of FPS and Joules and their implications for airsoft gameplay is crucial for players who want to enjoy the sport responsibly and safely. By adhering to legal limits, site restrictions, and proper gun selection, airsoft enthusiasts can ensure a thrilling and immersive experience without compromising safety or legality.

As you embark on your airsoft journey, remember to keep these concepts in mind and always prioritize responsible, safe, and legal gameplay. With a thorough understanding of FPS, Joules, and other essential airsoft principles, you’ll be well-equipped to make the most of your airsoft experience.

Typical FPS Measurements and Legal Limits

Airsoft guns come in various types and models, each with different FPS ratings. The legal limits for airsoft guns vary depending on your location, with different countries and regions enforcing specific restrictions on FPS and Joules to ensure player safety and adherence to local laws.

Many places in North America use the following criteria:

  • CQB/No minimum engage distance: 1.4 joules (~350FPS w/ 0.25g BB)
  • Minimum engage distance 50ft: 1.88 joules (~400FPS w/ 0.25g BB)
  • Minimum engage distance 100ft: 2.32 joules (~450FPS w/ 0.25g BB)

In the United Kingdom, the Policing and Crime Bill of 2017 established the following common airsoft site limits:

The permitted kinetic energy level is—

(a)in the case of a weapon which is capable of discharging two or more missiles successively without repeated pressure on the trigger, 1.3 joules;

(b)in any other case, 2.5 joules.”

What is an Airsoft Chrono and its Purpose?

An airsoft chrono, short for chronograph, is a device used to measure the velocity of airsoft guns. Its purpose is to ensure that airsoft guns are shooting within the acceptable limits of FPS (Feet Per Second) or Joules specified by field rules, event regulations, or local laws.

The Chrono provides a quantitative measurement of the velocity at which the airsoft BBs are propelled from the gun.

Many fields use a chrono to check every player’s Airsoft replica before the games start to ensure no one is shooting hot and to mark rifles that have a minimum engagement distance, like snipers.


Regulating FPS (Feet Per Second) and Joules in airsoft is important for safety reasons and to ensure a fair and balanced gameplay experience. Airsoft enthusiasts should also be mindful of the legal limits and restrictions in their region and ensure that their chosen airsoft guns adhere to these parameters.

The two main factors that affect the Joues are the velocity (FPS) and the weight of the BB. A 0.20g BB fired at 350 FPS has the same kinetic energy as a 0.32g BB shot at 275 FPS; both have ~1.13 Joules.

About the author

Nathan Skoczylas

When I'm not playing Airsoft I enjoy working out, training BJJ, mountain biking, and making music!