Convert measured arrow speed and calculate kinetic energy and momentum from the finished arrow weight. A separate rating mode explores illustrative adjustments; it does not predict your bow’s actual speed with a validated model.
Enter a chronograph reading. The starting 300 fps is an example, not a prediction.
Advanced options
Archery Trade Association: speed rating conditions. Verify the separate test conditions specified by your bow manufacturer before interpreting a rating.
How to use our Arrow Speed Calculator
- In "What do you want to calculate?", choose "Convert measured arrow speed" and enter "Measured arrow speed (fps)" plus "Arrow weight (grains)". The rating mode below is optional scenario arithmetic.
- For the rating scenario, match "Speed rating standard" to confirmed test conditions: ATA 70 lb/30 in/350 gr, legacy AMO 60 lb/30 in/540 gr, or the specifically confirmed 70 lb/30 in/350 gr IBO-labelled manufacturer setup.
- Enter your "Bow speed rating (fps)" exactly as listed for your bow under that standard.
- Enter your actual "Draw length (in)" (the bow setting or a shop measurement, not wingspan math).
- Enter your actual "Peak draw weight (lb)" at your current limb-bolt setting (not the max printed on the limbs).
- Enter total finished "Arrow weight (grains)" including point/broadhead, insert, nock, vanes, and shaft [1].
- Optional: Open Advanced options and enter "Weight on bowstring (grains)" for peep, D-loop, silencers, etc. If unsure, start with a small estimate and adjust later.
- Optional: Pick an "Adjustment rule set" (Conservative vs Typical) and your "Speed output unit" display preference.
- Click "Calculate".
- Check the speed and finished arrow weight. Rating-mode adjustments show the arithmetic of the selected assumptions; matching their expected direction does not validate the predicted speed.
Common mistakes and quick fixes
Mistake: Treating ATA and legacy AMO as the same standard. Fix: ATA uses 70 lb/30 in/350 gr; legacy AMO uses 60 lb/30 in/540 gr. Verify manufacturer test conditions before using any rating scenario.
Mistake: Using only the shaft weight for "Arrow weight (grains)" and forgetting the point/broadhead and other parts.
Fix: Enter the total finished arrow weight (complete arrow) [1]. If you are guessing, you will usually be closer by rounding up than rounding down.
Mistake: Entering draw length or draw weight from a catalog instead of your current bow settings.
Fix: Use your actual "Draw length (in)" and your actual "Peak draw weight (lb)" as the bow is set up today. Even small changes can move the estimate a lot.
Mistake: Leaving "Weight on bowstring (grains)" at 0 even though you have a peep, D-loop, and/or string silencers installed.
Fix: Add an estimate (for example, 10 to 20 grains) and compare the new result to the old one using the breakdown so you can see how sensitive speed is to string weight.
Mistake: A typo that makes the model unusable (for example 3300 fps, or 40 grains instead of 400), leading to N/A or a wildly high/low result.
Fix: Recheck each required field for a missing digit or wrong unit, then recalculate. If you still get N/A, bring the setup closer to the chosen standard or measure with a chronograph.
Mistake: Treating a rating scenario as guaranteed actual speed. Fix: Use a chronograph reading for energy or momentum calculations when actual performance matters.
Definitions
IBO-labelled rating: Confirm the manufacturer’s stated test setup. This page’s illustrative IBO scenario assumes 70 lb, 30 in and 350 gr, as used by some manufacturers; it is not a universal definition of IBO testing.
ATA speed rating uses 70 lb, 30 in and 350 gr. Legacy AMO uses 60 lb, 30 in and 540 gr; the two must not be combined under one label.
Bow speed rating (fps): The advertised speed in feet per second that your bow is rated at under the selected standard. The calculator starts from this number.
Draw length (in): How far the bow is set to draw, in inches. Ratings often assume 30 inches, so shorter draw lengths usually reduce estimated speed.
Peak draw weight (lb): The maximum draw weight your bow reaches, in pounds. Ratings assume a specific peak weight (often 70 lb for IBO).
Arrow weight (grains): Total finished arrow weight in grains (gr), including point/broadhead and all components [1].
Weight on bowstring (grains): Extra weight attached to the string (peep sight, D-loop, silencers, nock set). More string weight usually lowers speed.
Kinetic energy (ft-lbf, J): Energy of motion at launch, based on arrow weight and speed. It increases with speed squared, so a small speed change can noticeably change energy.
Momentum (slug-ft/s, kg-m/s): Mass times speed at launch. Heavier arrows can have higher momentum even if they are slower.
Speed adjustment breakdown: The list of fps added or subtracted for draw length, draw weight, arrow weight, and string/accessory weight based on the selected rule set.
Estimate reliability note: Identifies whether speed was supplied from a measurement or calculated from illustrative assumptions. No high, medium or low confidence classification is assigned.
Methodology
Overview: Measured mode converts your speed reading and computes energy and momentum. Rating mode applies explicit illustrative linear adjustments to a rating; these coefficients have not been validated for general bow prediction.
1) Scenario baselines: ATA is 30 in, 70 lb, 350 gr. Legacy AMO is 30 in, 60 lb, 540 gr. The IBO-labelled manufacturer scenario uses 30 in, 70 lb, 350 gr only when those are the stated manufacturer conditions.
2) Speed estimate (rating plus adjustments):
speed_est_fps = rating_fps + adj_draw_length + adj_draw_weight + adj_arrow_weight + adj_string_weight
adj_draw_length = (draw_length_in - baseline_draw_in) * k_dl
adj_draw_weight = (peak_draw_weight_lb - baseline_weight_lb) * k_dw
adj_arrow_weight = (baseline_arrow_gr - arrow_weight_gr) * k_ag
adj_string_weight = - string_accessory_weight_gr * k_sg
The selected "Adjustment rule set" supplies illustrative coefficients, shown in "Speed adjustment breakdown". They enable sensitivity comparisons, not validated actual-speed predictions. Energy from a scenario inherits that limitation.
3) Speed unit conversions:
speed_ms = speed_fps * 0.3048
speed_mph = speed_fps * (3600/5280)
speed_kmh = speed_ms * 3.6
4) Kinetic energy and momentum:
KE_ftlb = (arrow_weight_gr * speed_fps^2) / 450240
KE_J = KE_ftlb * 1.3558179483314004
mass_kg = arrow_weight_gr * 0.00006479891
p_kgms = mass_kg * speed_ms
mass_lb = arrow_weight_gr / 7000
mass_slug = mass_lb / 32.174
p_slugfps = mass_slug * speed_fps
Worked mini-example (numbers): Suppose you select IBO and enter rating_fps = 330, draw_length_in = 28, peak_draw_weight_lb = 60, arrow_weight_gr = 400, and string_accessory_weight_gr = 15. The calculator first computes each adjustment from the difference between your input and the IBO baseline (30 in, 70 lb, 350 gr), then adds them to 330 fps to get speed_est_fps. It then converts the speed and computes kinetic energy and momentum from that estimated speed.
Assumptions and limits: Measured mode assumes the speed reading and finished arrow mass apply to the same shot setup. Rating scenarios omit bow-specific efficiency and nonlinear effects, so neither profile provides a measured accuracy or confidence range. Follow the bow manufacturer’s minimum arrow-weight and operating requirements.