Crossbow Authority

Crossbow glossary

What Is FPS (Feet Per Second)?

FPS (Feet Per Second): The speed of a bolt as it leaves the crossbow, measured in feet per second.

By Marisol Vega, Senior Outdoor Equipment Writer & Research Editor. Manufacturer figures vary; check your crossbow's manual.

FPS is the standard unit for bolt speed. Advertised figures are usually measured by the manufacturer with a specific, often light, bolt, so real-world speed with a heavier hunting bolt is typically lower.

When comparing crossbows, check the bolt weight used for the rating and whether the figure is manufacturer-rated or independently measured.

Kinetic energy from speed and bolt weight

KE (ft-lbs) = bolt weight (grains) × FPS² ÷ 450,240

A 400-grain bolt at 350 FPS carries about 400 × 350² ÷ 450,240 ≈ 109 ft-lbs. At 400 FPS the same bolt carries about 142 ft-lbs, because speed is squared.

Why FPS matters

FPS is the headline number on almost every crossbow box. It affects trajectory, because a faster bolt drops less over a given distance, and it feeds into kinetic energy. But the printed figure is only useful if you know how it was measured.

Manufacturer speed ratings are normally achieved with a light bolt under ideal conditions. With the heavier bolts many people actually shoot, real speeds are lower, and the gap changes from model to model.

How to read it on a spec sheet

  • Find the bolt weight used for the rating. A 350 FPS claim with a 300-grain bolt is not comparable to 350 FPS with a 400-grain bolt.
  • Separate manufacturer-rated figures from independently measured ones. On this site rated and measured numbers are always labelled.
  • Look at consistency as well as the top number: shot-to-shot variation matters for accuracy.

Common mistakes

  • Buying on the FPS number alone. Speed is one input to trajectory and energy, and a fast crossbow that is difficult to cock or shoot accurately may not suit you.
  • Ignoring bolt weight. Heavier bolts are slower but often retain energy better and may be needed to meet local rules.

In my testing

Speed is the first thing I measure. I shoot several strings over a chronograph with a stated bolt weight and report the range I saw next to the manufacturer’s rating, so you can see the difference. How I test.

Frequently asked questions

Why is my crossbow slower than the box says?

Rated speeds are usually recorded with a very light bolt. A heavier hunting bolt, different nocks, string wear or a lack of lubrication will all lower measured speed.

Does higher FPS mean a flatter trajectory?

Generally yes over a given distance, but bolt weight, drag and sight setup also affect where the bolt lands. A reticle must be matched to the speed range of the crossbow.

How do I measure my own FPS?

A chronograph placed at a safe, controlled distance is the standard tool. Follow the chronograph’s instructions and shoot only in a safe location with a proper backstop.

Is there a legal minimum FPS for hunting?

Some jurisdictions specify draw weight, energy or bolt requirements. These change, so check the current rules from your wildlife authority.

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Definitions are general information. Always follow your crossbow manufacturer's manual, and verify local laws with the relevant authority.