Arrow Speed Calculator — How Fast Does an Arrow Travel?
This arrow speed calculator allows you to accurately determine the speed of an arrow. While it is based on the bow speed IBO specification, you can input the individual settings of your bow. It will give you a rough idea of how fast an arrow travels after changing the bow from the recommended specifications.
Understanding Bow Speed IBO Specification
Most professional bows use the IBO (International Bowhunting Organization) specification. This specification determines the arrow speed, provided that you keep the following parameters:
- Draw length equal to 30 inches;
- Draw weight equal to 70 pounds; and
- Arrow weighing 350 grains.
If you deviate from these parameters, the arrow speed will not equal the one given by the specification. Nevertheless, most archers do not use these exact parameters. This is where this bow speed calculator comes in handy — it allows you to examine how the arrow will behave under a different bow setting.
Archery Calculator Principles
You should adjust the arrow speed given by the IBO specification according to the following rules:
- For every inch of draw length under 30", subtract 10 ft/s from the IBO value.
- For every inch of draw length above 30", add 10 ft/s to the IBO value.
- For every 3 grains of total arrow weight above draw weight × 5, subtract 1 ft/s from the IBO value.
- For every 3 grains of additional weight on the bowstring, subtract 1 ft/s from the IBO value.
All of these rules can be put in one common equation:
v = IBO + (L − 30) × 10 − W/3 + min(0, −(A − 5D)/3)
Where:
- v — Actual arrow speed in ft/s;
- IBO — Arrow speed according to the IBO specification in ft/s;
- L — Draw length in inches;
- W — Additional weight on the bowstring in grains;
- A — Arrow weight in grains; and
- D — Draw weight in pounds.
Momentum and Kinetic Energy
You can also use the arrow speed calculator to find the momentum and the kinetic energy of the arrow. These are calculated as follows:
Momentum (lb·s) = (Arrow weight in grains × Speed in ft/s) / 225,218
Kinetic Energy (ft·lb) = (Arrow weight in grains × Speed in ft/s²) / 450,240
To convert to SI units:
- Momentum (kg·m/s) = Momentum (lb·s) × 4.44822
- Kinetic Energy (J) = Kinetic Energy (ft·lb) × 1.35582
The arrow speed calculator converts all units automatically. If you try to do all of these calculations by hand, keep in mind what units you actually use!
Metric and Imperial Units
This calculator supports both imperial units (inches, pounds, grains) and metric units (centimeters, kilograms, grams). When you select the metric system, the inputs are automatically converted to imperial units for the IBO formula calculation, and all results are shown in both systems.
Frequently Asked Questions (FAQs)
What is IBO speed?
IBO speed is the arrow velocity measured under standardized conditions set by the International Bowhunting Organization: 30-inch draw length, 70-pound draw weight, and a 350-grain arrow. Most bow manufacturers advertise this rating on their products.
How much does draw length affect arrow speed?
Each inch of draw length away from 30 inches adds or subtracts approximately 10 ft/s. For example, a 28-inch draw will reduce the IBO-rated speed by 20 ft/s.
How much does arrow weight affect speed?
Arrow weight only affects speed if it exceeds 5 times the draw weight in pounds (e.g., for a 70 lb bow, the threshold is 350 grains — exactly the IBO standard). Each 3 additional grains above this threshold reduces the speed by 1 ft/s.
Why does bowstring weight matter?
Any extra weight on the bowstring (silencers, accessories) reduces arrow speed by 1 ft/s for every 3 grains of added weight, because the bow must accelerate that extra mass along with the arrow.
What kinetic energy is needed for hunting?
Common guidelines for hunting are: small game — 25 ft·lb minimum; medium game (deer) — 40–55 ft·lb; large game (elk, bear) — 65–80 ft·lb. These are general recommendations and may vary by jurisdiction and conditions.