Arrow Speed Calculator (Real FPS from IBO)
Estimate real arrow speed by subtracting 10 fps per inch of draw under 30, 2 fps per pound under 70, and 1 fps per 3 grains of arrow weight over 350 from your bow's IBO rating.
The speed printed on a bow is measured under conditions almost nobody shoots: 30 inch draw, 70 pounds, and a 350 grain arrow on a bare string. This calculator walks that number back to your actual setup so you can size a sight tape, estimate trajectory, or just find out how much of that 340 fps you were ever going to see.
The formula, term by term
Every published IBO derating rule is a linear approximation of something that is not quite linear, but across the range archers actually shoot they hold up well. The four terms:
- Draw length: 10 fps per inch. Subtract 10 for every inch under 30, add 10 for every inch over. This is the largest single factor and the reason a short-draw archer will never see the sticker number.
- Draw weight: 2 fps per pound. Subtract 2 for every pound under 70. Turning a 70 pound bow down to 60 costs about 20 fps before anything else is counted.
- Arrow weight: 1 fps per 3 grains. Subtract 1 fps for every 3 grains over 350. A 420 grain arrow is 70 grains over the standard, costing roughly 23 fps.
- String accessories: 3 to 14 fps. A peep, a d-loop, silencers and a kisser all add mass that has to accelerate with the string, and string mass is the most expensive mass on a bow.
Note that all four subtract. It is almost impossible for a real setup to beat its IBO rating, because IBO is by construction the fastest legal combination of conditions. The rare exception is an archer with a draw length over 30 inches, who genuinely does gain about 10 fps per inch.
What each factor costs
| Change | Speed effect | What it costs or buys elsewhere |
|---|---|---|
| 1 inch shorter draw | about -10 fps | Usually improves accuracy, which is why short is the safer error |
| 5 lb less draw weight | about -10 fps | Easier to hold, better form under fatigue |
| 25 grains more arrow | about -8 fps | Quieter, more momentum, higher FOC if added at the point |
| 100 grains more arrow | about -33 fps | A different arrow philosophy entirely |
| Adding a peep sight | about -3 fps | Non-negotiable for a compound with a sight |
| Adding string silencers | -3 to -6 fps | Meaningfully quieter shot |
| Aggressive cam over smooth cam | +10 to +20 fps | Harsher draw cycle, less forgiving |
Why the estimate and the chronograph disagree
Expect the real number to come in 5 to 10 fps below the estimate on a well-maintained bow, which is why the calculator shows a range rather than a single figure. The causes are all mundane: strings and cables creep over their life and change cam timing, brace height drifts, rest contact steals a little energy, and manufacturer test bows are set up perfectly by people who set up bows all day.
A gap of 20 fps or more is a signal rather than a disappointment. It usually means cam timing has drifted, the string has stretched enough to shorten the draw and lower the peak weight, or the bow is not actually set to the poundage marked on the limb bolts. All three are pro shop jobs and all three are worth fixing regardless of speed.
A ready-to-hunt package rated in the low 300s at IBO will, for a 28 inch draw archer at 60 pounds with a 420 grain arrow, land somewhere around 250 fps in the real world. That is entirely adequate for practical shot distances, and it is a useful reminder that the flagship bows quoting 340 or 350 IBO are subject to exactly the same subtractions. Bows with wide draw weight and draw length adjustment are usually the better buy, because fitting beats fps.
Speed is not the goal, and here is why
The genuine argument for arrow speed is range error forgiveness. A flatter trajectory means misjudging 40 yards for 35 costs you less vertical error. That is a real advantage and it is the only one worth paying for.
What speed does not buy is group size. Fast bows tend to run aggressive cams with steep force draw curves, which are harsher to hold and less tolerant of an imperfect release. Speed also comes from light arrows, and light arrows are louder, retain less energy downrange, and sit closer to the 5 grain per pound safety floor. The archer who ranges the target exactly gets all the benefit of a fast bow without owning one, which is why a rangefinder outranks 20 fps for almost everybody. Our rangefinder roundup covers what to look for.
Once you have a speed number you trust, it feeds two other calculations directly: the kinetic energy calculator, which needs velocity to return anything meaningful, and the sight tape calculator, which uses speed to predict pin gaps. Both are only as accurate as the fps you feed them, so a chronograph session at a pro shop pays for itself.
Recurve and traditional speeds
IBO ratings are a compound convention and do not transfer. A recurve at 45 pounds with a normal wood or carbon arrow typically shoots in the 170 to 200 fps range, and a longbow slower still. The derating rules above do not apply, because a recurve stores energy along a completely different force draw curve with no let-off. Traditional archers who want a real number need a chronograph, and most find it lower than they expected. That is not a problem: at traditional distances, momentum and shot placement carry the work.
Related tools
- Total arrow weight calculator: the grain figure this calculator needs
- Draw length calculator: the single biggest speed variable
- Angle compensation calculator: where trajectory actually bites
- Kinetic energy calculator: turn fps into foot-pounds
Frequently asked questions
How do I estimate arrow speed from an IBO rating?
Start with the IBO number, subtract 10 fps for every inch your draw length is under 30, subtract 2 fps for every pound under 70, subtract 1 fps for every 3 grains of arrow weight over 350, then subtract for string accessories. A 340 IBO bow at 29 inches, 60 pounds, with a 420 grain arrow and a peep and loop lands around 282 fps.
What is IBO speed measured at?
A 30 inch draw length, 70 pounds of draw weight, and a 350 grain arrow, which is the 5 grains per pound minimum for a 70 pound bow. The string carries no accessories. Almost nobody shoots that combination, which is why the number on the bow is not a lie but is not your speed either. It is a standardised comparison figure between bows.
Why is my chronograph reading slower than the calculator?
Manufacturer test conditions are ideal and the estimate ignores several real losses: string and cable wear, cam timing that has drifted, a slightly out of spec brace height, arrow rest contact, and temperature. A gap of 5 to 10 fps is normal and not a fault. If you are 20 fps or more below the estimate, have the bow checked for timing and string stretch rather than adjusting your expectations.
How much speed does a peep sight cost?
A peep alone typically costs 2 to 4 fps, a d-loop another 1 to 2, and string silencers or dampeners 3 to 6 more depending on size and placement. The mechanism is simple: anything you add to the string has to be accelerated with it, and mass on the string is far more costly than mass on the riser. A fully dressed string commonly costs 8 to 14 fps.
Is a faster bow more accurate?
No. Speed reduces the penalty for misjudging distance, which is a real advantage in the field, but it does nothing for group size and aggressive fast cams are usually harsher to shoot and less forgiving of a poor release. Most archers gain more accuracy from a correct draw length and a rangefinder than from 20 fps, and heavier arrows are quieter and retain energy better.
What is the difference between IBO and ATA speed ratings?
Both are measured at 30 inches, 70 pounds and 350 grains, but the ATA protocol permits a small amount of string equipment where IBO specifies a bare string. In practice an ATA figure usually reads a few feet per second slower than an IBO figure for the same bow. Compare bows against ratings from the same standard, never an IBO number against an ATA one.
How we choose: we compare published manufacturer specifications, verified owner reviews, and pro shop guidance. We do not test gear in person. Draw weight and arrow spine affect safety, so follow your bow manufacturer's specifications and have setup work checked by a qualified pro shop.