Every compound bow is sold with a speed rating, and almost nobody shoots that speed. The rating is a laboratory figure produced under a fixed set of conditions that were chosen to make bows comparable to each other, not to describe any particular archer. Change the draw length, the draw weight or the arrow, and the real number moves — often by fifty or sixty feet per second. This calculator applies the archery industry's standard adjustment rules of thumb to a published rating so you can see roughly where your own setup lands.
The important framing, which Arb Digital would rather state up front than bury: what comes out of this page is an estimate derived from published conventions. It is not a measurement, and it is not a manufacturer's specification for your bow. A chronograph reading taken at a pro shop, with your arrows, is the only figure that describes your equipment. Use this to understand which variables matter and roughly how much, then go and measure.
What This Arrow Speed Calculator Does
It starts from a bow's published speed rating and adjusts it for four things the rating standard held fixed: draw length, peak draw weight, arrow weight and the mass hung on the string. It then reports the arrow's kinetic energy and momentum at that estimated speed, plus grains per pound of draw and the total change from the published number, so you can see how much of the rating survived contact with a real setup.
Crucially, it asks which rating standard the number came from. IBO and ATA ratings are measured under different standard conditions, so the same bow is legitimately described by two different figures, and mixing them up is the fastest way to get a nonsense answer. The Archery Trade Association maintains the ATA/AMO measurement standard used across the industry.
How to Use It
- Pick the rating standard. Manufacturers usually print IBO figures because they are higher. If the spec sheet says ATA or AMO, switch the selector, because the baseline arrow weight and draw weight the calculation corrects from are different.
- Enter the published rating. Use the number for your exact model, cam and module, not a general figure for the model family.
- Enter your draw length and peak draw weight. Draw length must be the bow's set draw length measured to the industry standard, which is not the same as an estimate from your arm span.
- Enter the finished arrow weight. Weigh a completed arrow on a grain scale — shaft, point, insert, nock and fletching together. Our arrow FOC calculator adds those components up if you do not have a scale to hand.
- Add anything clamped to the string. A peep, a loop, nock sets and silencers all cost speed, and their combined weight is easy to underestimate.
The Formula and How It Is Calculated
The adjustments are published rules of thumb that have been used across the archery trade for decades. Each one describes how far the speed moves for a unit change away from the rating standard:
- Draw weight: about 2 fps for every pound above or below the standard's draw weight.
- Draw length: about 10 fps for every inch above or below 30 inches.
- Arrow weight: about 1 fps lost for every 3 grains the arrow exceeds the standard's baseline, which is defined as a fixed number of grains per pound of draw — 5 gr/lb under IBO, 7 gr/lb under ATA.
- String weight: about 1 fps lost for every 3 grains added to the string.
Worked through with the values loaded on this page, using the IBO standard: a 340 fps rating, a 28-inch draw, 60 lb peak weight, a 400-grain arrow and 15 grains on the string. The IBO baseline arrow for a 60-pound bow is 5 × 60 = 300 grains. Draw weight costs 2 × 10 = 20 fps, draw length costs 10 × 2 = 20 fps, the extra 100 grains of arrow costs 100 ÷ 3 = 33.3 fps, and the string hardware costs 5 fps. That is 78.3 fps of loss, leaving roughly 262 fps.
Kinetic energy uses the standard archery form KE = m v² ÷ 450,240 with mass in grains and speed in feet per second, which returns foot-pounds. Momentum uses p = m v ÷ 225,218 for slug feet per second. Both constants simply fold in the 7,000 grains per pound and the acceleration due to gravity. The general physics behind them lives in our kinetic energy calculator and momentum calculator.
IBO and ATA Ratings Are Measured Differently
This is the point most speed discussions get wrong. The IBO standard measures a bow at a 30-inch draw length, 70 pounds of peak draw weight, and a 350-grain arrow — five grains of arrow for every pound of draw. The ATA/AMO standard measures at the same 30-inch draw but at 60 pounds with a 420-grain arrow, which is seven grains per pound. A heavier arrow on a lighter bow produces a lower number, so an ATA figure for a given bow will always sit well below its IBO figure.
Neither is wrong and neither is marketing spin; they are two conventions with different purposes, and the ATA figure is closer to what most people actually shoot because seven grains per pound is nearer a typical real-world setup. The mistake is comparing an IBO rating for one bow against an ATA rating for another and concluding one is faster. If you are shopping, get both bows' figures on the same standard, or use this calculator to bring them to a common setup.
Why the Rules of Thumb Are Only Approximations
Each adjustment above is a linear approximation of something that is not linear. Cam efficiency, for instance, is not constant across the draw length range: the same bow set to 26 inches is not simply three inches' worth of speed below the same bow at 29 inches, because the cam geometry that stores energy through the draw cycle changes with the module. The 10 fps per inch figure is a decent average across a normal range and gets less trustworthy at the extremes of a bow's adjustment.
The arrow weight rule has a similar limitation. Adding mass to an arrow makes the bow more efficient at transferring stored energy, which is why a heavier arrow loses less speed than a naive energy calculation would suggest and why it can carry more total energy despite being slower. The 1 fps per 3 grains convention already has that efficiency gain baked into it as an average, but the real curve flattens as arrows get very heavy. Treat the estimate as reliable within a normal setup window and increasingly rough outside it.
Speed Is Not the Only Thing, and Often Not the Main Thing
A faster arrow flattens the trajectory, which forgives range estimation errors. That is a genuine advantage and it is the reason speed ratings sell bows. But the same change that adds speed — a lighter arrow — reduces kinetic energy and momentum at the target, makes the bow louder and harsher to shoot, increases hand shock, and gives the arrow less resistance to crosswind at distance. The results grid on this page reports energy and momentum alongside speed for exactly that reason.
There is also a hard floor. Bow manufacturers publish a minimum arrow weight, usually expressed in grains per pound of draw, and shooting below it can damage the bow and voids the warranty. Five grains per pound is the common minimum, which is why the IBO standard sits exactly there — the rating is measured at the lightest arrow the bow is rated for. The grains-per-pound figure in the results grid is there so you can check your setup against your own manufacturer's stated minimum.
Let-Off, Draw Cycle and What This Calculator Does Not Model
Let-off is the percentage by which holding weight drops at full draw, and a high let-off bow feels dramatically easier to hold. It is not in the speed calculation because it does not directly set the stored energy; what matters is the area under the whole force-draw curve, and two bows with the same peak weight and the same let-off can still store different amounts of energy depending on how aggressive the draw cycle is. That is a real difference between bows that no simple adjustment rule can capture, and it is one reason two bows with identical IBO ratings can chronograph differently with the same arrow.
Also absent: string material and strand count, cam timing, the state of the string's wear, arrow rest type and the fletching's drag. All of these move the number by a few feet per second each. Their combined effect is easily larger than the difference between two bows on a spec sheet, which is another argument for a chronograph over arithmetic. Bow setup, cam timing and draw length adjustment are jobs for a qualified bow technician with a press, not for a spreadsheet.
Turning Speed Into Something You Can Aim With
A speed figure only becomes useful when it turns into a sight tape or a pin gap. Arrow speed sets how much the arrow drops between marked distances, and small speed errors compound at longer ranges. If you build a sight tape from an estimated speed rather than a chronographed one, the near pins will look fine and the long pins will be visibly wrong, which is exactly the pattern that sends archers back to the shop. The estimate on this page is a good sanity check on a chronograph reading and a poor substitute for one.
For competition, the equipment rules published by World Archery govern what bows, sights and arrows are permitted in each division, and they are worth reading before investing in a setup for a scored event. Speed is unregulated in most compound divisions, but arrow diameter, sight type and release aids are not.
Arb Digital builds free technical calculators like this one for specialist retailers, then earns them search visibility for the exact terms buyers use when they are comparing equipment and close to a decision.
SEO Services Talk to Arb DigitalCommon Mistakes to Avoid
- Mixing IBO and ATA figures. They are measured at different draw weights and arrow weights. Comparing one against the other tells you nothing about which bow is faster.
- Using a nominal draw length. The bow's set draw length to the industry standard is what matters, and it is often an inch away from what an archer assumes it is.
- Forgetting the string hardware. A peep, loop, nock set and silencers together can easily reach 25 grains, which is another 8 fps off the estimate.
- Chasing speed below the minimum arrow weight. Manufacturers publish a minimum grains-per-pound figure. Going under it can damage the bow and voids the warranty.
- Building a sight tape from an estimate. Small speed errors are invisible at 20 yards and obvious at 60. Chronograph the setup before marking a tape.
Related Free Tools From Arb Digital
Pair this with the arrow FOC calculator to build the arrow weight this page needs, and the draw length calculator for the measurement that sets your bow up in the first place. For the underlying physics, use the kinetic energy calculator, the momentum calculator and the projectile motion calculator. The speed converter handles feet per second to metres per hour and back. Everything else is in the free online tools hub.
Frequently Asked Questions
IBO measures a bow at a 30-inch draw, 70 pounds peak weight and a 350-grain arrow. ATA/AMO measures at a 30-inch draw, 60 pounds and a 420-grain arrow. The heavier arrow on the lighter bow makes the ATA figure lower, so the same bow legitimately carries two different numbers.
The published rule of thumb is about 10 feet per second per inch away from the 30-inch rating standard. It is an average across a normal adjustment range and becomes less accurate at the extremes of a bow's draw length settings.
Roughly 1 foot per second for every 3 grains above the rating standard's baseline arrow. That baseline is 5 grains per pound of draw weight under IBO and 7 grains per pound under ATA.
Yes. A peep sight, string loop, nock sets and silencers all have to be accelerated with the arrow. The convention is about 1 foot per second lost for every 3 grains added to the string, and a fully dressed string can easily carry 25 grains.
No. Small errors in speed are invisible at short distance and clearly wrong at long distance. Use a chronograph reading taken with your own arrows to mark a tape, and use this page only as a sanity check on that reading.
Let-off describes how much holding weight drops at full draw, not how much energy the bow stores. Stored energy depends on the whole force-draw curve, which no simple adjustment rule captures, so two bows with the same rating and let-off can still chronograph differently.
No. A lighter, faster arrow flattens trajectory but carries less kinetic energy and momentum, makes the bow louder and harsher, and is more affected by crosswind at distance. The results grid shows energy and momentum next to speed for that reason.
Manufacturers publish their own minimum, usually expressed as grains per pound of peak draw weight, and 5 grains per pound is a common figure. Shooting below the stated minimum can damage the bow and typically voids the warranty, so check your own manual.
The figures on this page are estimates built from published industry rules of thumb, not measurements of any particular bow. Only a chronograph reading with your own arrows describes your equipment, and bow setup, cam timing and draw length adjustment should be carried out by a qualified bow technician following the manufacturer's own specifications.
