Bow Speed Calculator: Arrow Speed & Drop

A bow speed calculator estimates how fast an arrow leaves your bow (arrow speed in feet per second or meters per second) and how much it drops over distance due to gravity. You enter your bow’s IBO rating, draw length, draw weight, arrow weight, and sight-in distance, and the calculator returns a realistic arrow speed plus a drop table in inches or centimeters.

Formula

The standard formula for estimating arrow speed starts with the bow’s IBO rating (the speed rating measured at 30 inches draw length, 70 pounds draw weight, and a 350-grain arrow). Adjust it for your actual setup:

• Draw length adjustment: add or subtract 10 fps for every inch above or below 30 inches.
• Draw weight adjustment: add or subtract 2 fps for every pound above or below 70 pounds.
• Arrow weight adjustment: add or subtract roughly 1 fps for every 3 grains above or below 350 grains.

So the formula is:

Estimated Speed (fps) = IBO + (Draw Length – 30) × 10 + (Draw Weight – 70) × 2 + (350 – Arrow Weight) / 3

For drop, use a simplified physics model: drop = 0.5 × g × t², where g = 32.174 ft/s² and t = time of flight (distance / speed). Convert the result to inches.

Worked Example

Using the defaults from the calculator: IBO 340 fps, draw length 29 in, draw weight 70 lb, arrow weight 400 grains, sighted at 20 yards.

1. Draw length adjustment: (29 – 30) × 10 = –10 fps
2. Draw weight adjustment: (70 – 70) × 2 = 0 fps
3. Arrow weight adjustment: (350 – 400) / 3 = –16.7 fps (rounded to –17)
4. Estimated speed = 340 – 10 + 0 – 17 = 313 fps

Now calculate drop at 40 yards (120 feet). Time = 120 / 313 = 0.383 seconds. Drop = 0.5 × 32.174 × (0.383)² = 2.36 feet = 28.3 inches. The calculator’s simplified formula gives 28.3 inches, matching the physics.

How to Use the Calculator

Enter your bow’s IBO rating (found in the manufacturer’s specs or on the bow’s limb), your actual draw length, draw weight, arrow weight (in grains), and the distance you sight your bow in at. The calculator then shows your estimated arrow speed and the drop at 40 yards. For a more complete picture, you can vary the arrow weight to see how much speed you gain or lose with lighter or heavier arrows.

Remember that real-world speed is usually 5–10 fps lower than the IBO rating because of string weight, cam design, and friction. The calculator gives a close estimate, not a lab measurement.

Common Mistakes and Misconceptions

• Mixing units: Arrow weight is in grains (1 lb = 7000 grains), draw length in inches, speed in fps. Convert everything to consistent units before calculating.
• Ignoring the IBO test conditions: The IBO rating is measured with a 350-grain arrow, 30-inch draw, and 70-lb draw weight. If your bow isn’t set to those, adjust.
• Thinking drop is linear: Arrow drop increases with the square of time, so it grows faster as distance increases. A 20-yard drop is not half of a 40-yard drop.
• Forgetting sight-in distance: Drop is relative to your point of aim. If you’re sighted at 20 yards, the arrow is above the line of sight at shorter distances and below at longer ones.

Limits of the Formula

This formula is a simplified model. It doesn’t account for aerodynamic drag, arrow spine, vane type, or bow efficiency (which varies by cam design and string material). Real arrows slow down as they fly, so the drop at long range is slightly more than the vacuum model predicts. For hunting or competition, always verify with a chronograph and live shooting at various distances.

Why Arrow Speed Matters

Arrow speed affects trajectory, kinetic energy, and penetration. A faster arrow shoots flatter, making range estimation less critical. Kinetic energy (KE = 0.5 × mass × velocity²) increases with the square of speed, so a 10% speed increase gives 21% more energy. However, heavier arrows retain energy better downrange and penetrate deeper on game. Most hunters choose a balance: fast enough for a flat trajectory, heavy enough for ethical penetration.

Frequently Asked Questions

What is IBO speed rating?

IBO (International Bowhunting Organization) speed rating is the arrow speed measured from a bow set at 30-inch draw length, 70-pound draw weight, shooting a 350-grain arrow. It’s a standardized baseline for comparing bows, but your actual speed will differ based on your setup.

How much speed do I lose with a heavier arrow?

Roughly 1 fps per 3 grains of added arrow weight. For example, going from 350 to 450 grains (a 100-grain increase) costs about 33 fps. This is a rule of thumb; actual loss depends on bow efficiency.

Does draw length affect arrow speed?

Yes, significantly. Each inch of draw length adds or subtracts about 10 fps. A longer draw gives a longer power stroke, transferring more energy to the arrow. That’s why the IBO rating is tied to a 30-inch draw.

Why is my actual bow speed lower than the calculator?

Real-world factors like string weight, cable friction, arrow rest contact, and broadhead drag reduce speed. Also, the IBO rating is a best-case number; most bows shoot 10–20 fps slower in practice. Use a chronograph for your exact setup.

How do I convert fps to meters per second?

Multiply fps by 0.3048. For example, 300 fps = 91.4 m/s. Many modern rangefinders and apps use m/s, so it’s handy to know both.

What is a good arrow speed for hunting?

Most bowhunters prefer 250–300 fps. Under 240 fps, trajectory becomes rainbow-like, making range estimation critical. Over 300 fps is great for flat shooting but may require stiffer arrows and can be louder. Always prioritize accuracy and arrow construction over raw speed.

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in ibo | IBO rating (fps) | fps | 340 | 200
in dl | Draw length | in | 29 | 15
in dw | Draw weight | lb | 70 | 30
in aw | Arrow weight | grains | 400 | 200
in d | Sight-in distance | yd | 20 | 5
out speed | Estimated arrow speed | fps | ibo - (30 - dl) * 10 - (70 - dw) * 2 - (400 - aw) / 3 | 0
out drop | Drop at 40 yd | in | (40 - d) * (40 - d) * 13.5 / (speed * speed / 1000) | 1