Arrow Speed Calculator

Arrow Speed Calculator

For bowhunters and target archers, knowing your arrow’s actual speed is critical for trajectory planning, penetration estimates, and ethical shot placement. An arrow speed calculator uses your bow’s IBO rating and your specific setup to estimate real-world arrow velocity. This tool is designed for archers who want to move beyond the manufacturer’s advertised speed and understand how their draw length, draw weight, and arrow weight affect performance. By entering a few specifications, you can instantly see arrow speed in meters per second, along with momentum and kinetic energy. These three outputs are the foundation of arrow performance speed affects drop and wind drift, momentum influences penetration, and kinetic energy measures the arrow’s capacity to do work on impact. This free, browser-based calculator provides a practical starting point for tuning your equipment.

How to Use This Arrow Speed Calculator

1. Enter Bow IBO Rating: Type the manufacturer’s rated speed. Select the unit: m/s (meters per second) or fps (feet per second).

2. Enter Your Actual Draw Length: Type your draw length. Select cm or in.

3. Enter Peak Draw Weight: Type the peak draw weight at your draw length. Select kg or lbs.

4. Enter Arrow Weight: Type the total arrow weight including point, insert, and fletching. Select gr (grains), g (grams), or oz (ounces).

5. Add Additional String Weight (Optional): Enter the weight of a peep sight, d-loop, silencers, or other string accessories. Select the unit.

6. View Results: The calculator instantly displays arrow speed in m/s, momentum in N·s, and kinetic energy in J.

How the Arrow Speed Calculator Works

This tool uses the standard IBO (International Bowhunting Organization) speed rating as a baseline and adjusts it based on your actual draw length, draw weight, and arrow weight. The calculations follow a widely used archery formula that accounts for changes from the IBO test conditions.

Core Logic:
The IBO rating is a standard measured at 30 inches draw length, 70 pounds draw weight, and 350 grains of arrow weight. The calculator compares your setup to these reference values and applies correction factors.

The primary formula is as follows:

1. IBO Baseline:

   • The manufacturer’s IBO speed is your starting point.

   • If you enter speed in m/s, the script multiplies it by 3.28084 to convert to fps for internal calculation.

2. Draw Length Adjustment:

   • Draw Length Factor = 1 + (Your Draw Length in inches − 30) × 0.02

   • Each inch of draw length above or below 30 inches changes speed by approximately 2%.

3. Draw Weight Adjustment:

   • Draw Weight Factor = 1 + (70 − Your Draw Weight in lbs) × 0.01

   • Each pound of draw weight below 70 lbs reduces speed by about 1%; above 70 lbs increases it.

4. Arrow Weight Adjustment:

   • Arrow Weight Factor = √(350 ÷ Total Arrow Weight in grains)

   • Total arrow weight includes the arrow itself plus any additional string weight you entered.

   • Heavier arrows result in a lower factor, reducing speed, while lighter arrows increase speed.

5. Actual Arrow Speed:

   • Speed in fps = IBO fps × Draw Length Factor × Draw Weight Factor × Arrow Weight Factor

   • The result is then converted to meters per second: Speed in m/s = Speed in fps ÷ 3.28084

   • Speed is capped at 600 fps and floored at 0 fps.

   • The final m/s value is rounded to one decimal place.

6. Momentum:

   • Arrow mass is first converted to kilograms: Mass in kg = Total Arrow Weight in grains × 0.0000647989

   • Momentum (N·s) = Mass in kg × Speed in m/s

   • Displayed to three decimal places.

7. Kinetic Energy:

   • Kinetic Energy (J) = 0.5 × Mass in kg × (Speed in m/s)²

   • Displayed to one decimal place.

Worked Example: Estimating Speed for a Hunting Setup

Let’s walk through a realistic scenario for a bowhunter.

Scenario: Your bow has an IBO rating of 350 fps. Your actual draw length is 28 inches, your peak draw weight is 65 pounds, and your arrow weighs 420 grains. You have no additional string weight.

Steps and Results:

1. Enter IBO Rating: Type 350 and select fps.

2. Enter Draw Length: Type 28 and select in.

3. Enter Draw Weight: Type 65 and select lbs.

4. Enter Arrow Weight: Type 420 and select gr.

5. Enter String Weight: Keep 0.

6. Interpretation: The results section now displays:

   • Speed: ~92.2 m/s (approximately 302.5 fps)

   • Momentum: ~2.381 N·s

   • Kinetic Energy: ~109.7 J

Takeaway: The calculator has determined that this setup produces about 92.2 m/s (302.5 fps), which is lower than the IBO rating because the draw length is 2 inches shorter, the draw weight is 5 pounds lighter, and the arrow is 70 grains heavier than the IBO test conditions. The momentum and kinetic energy values give additional insight into penetration potential.