Kinetic Energy, Momentum & Pass-Through Calculator

Both describe what a moving arrow carries, but they weight speed and mass differently. Kinetic energy leans hard on speed — speed counts twice over, mass only once — so a light fast arrow flatters it. Momentum treats the two evenly, so weight counts for much more.

That's why the same two arrows can swap places depending on which number you look at, and it's the whole light-versus-heavy argument in a nutshell. Energy is the better guide to what happens on impact — breaking through the near shoulder, driving a wide mechanical open. Momentum is the better guide to what happens after impact, when the arrow is fighting resistance the whole way through. Bowhunters who care about pass-throughs quote momentum, and they have good reason to.

Switch the chart to Light vs heavy arrow and something worth knowing shows up. Hold the bow constant and walk the arrow weight up: energy hardly moves across the middle of the range, while momentum climbs steadily the whole way. A heavier arrow leaves slower, but it captures more of what the bow put in, and the two effects very nearly cancel on the energy figure.

So the honest version of the argument isn't "heavy arrows trade energy for momentum" — it's that within a sensible range they cost you very little energy and hand you a good deal of momentum. What they genuinely do cost is trajectory: a heavier arrow drops more, and that's the trade you're really making. The Trajectory Visualizer is where you can see that side of it.

Check it: a 450 gr arrow at 280 fps reads about 78 ft·lb and 0.559 slug·ft/s. Any published arrow-energy chart will agree, because there's nothing to argue about here.

An arrow starts slowing the instant it leaves the string, and it never gets any of that back. Every energy figure quoted at the bow is a launch number, but the animal is standing 30 or 40 yards away — so the only figure worth acting on is the one at that distance.

How fast the speed bleeds off comes down to how much surface is hanging in the air. Low-profile vanes give up the least, hunting vanes a little more, four vanes or full helical more again, and long feathers the most. Broadheads add their own share, with wide fixed blades costing more than a slim two-blade. All of it is treated as a steady percentage lost per yard, so the far half of a long shot costs proportionally more than the near half.

Check it: 450 gr at 280 fps with hunting vanes and a three-blade head arrives at 40 yd doing about 243 fps. Energy has fallen from 78 to roughly 59 ft·lb — a quarter of it gone before the arrow ever touches hair. That gap is the single most useful thing on this page.

FOC describes how far forward the arrow's balance point sits. Weight up front keeps the shaft pointing where it's going, both in flight and — the part that matters here — while it's driving through tissue. An arrow that stays straight puts all its momentum in one direction; one that starts to yaw wastes it sideways.

The direction of the effect isn't controversial. The size of it very much is. Some of the strongest claims for extreme FOC come from a small body of testing that hasn't been widely replicated, and plenty of experienced hunters report far more modest gains. This tool deliberately takes the cautious side: FOC moves the penetration figure, but nowhere near as much as the boldest claims would suggest.

Check it: if you want to see the difference yourself, shoot the same shaft into a dense target with a 100 gr head and then a 200 gr head, matching total arrow weight with tape or inserts so only the balance point changes. That test is worth more than any argument online — including this one.

Heads differ in how much of the arrow's momentum they spend getting through. A narrow two-blade that cuts from first contact wastes the least — there's no tip to push a hole open before the blades start working. Three- and four-blade fixed heads cut more tissue and cost more to drive. Mechanicals cost the most of all, because part of the arrow's momentum goes into opening the blades before any cutting starts, and a wide cutting diameter drags harder the whole way through.

The ranking is settled — you'll find very little disagreement on the order. The spacing between them is this tool's own calibration, set so the outputs land where bowhunters' collective experience puts them. Treat a change of one step as meaningful and the exact percentage as approximate.

None of this makes mechanicals a bad choice. On a fast bow with plenty of momentum in hand, at deer-class ranges, the bigger hole is a real advantage and the cost is affordable. The trouble comes when a wide mechanical is bolted onto a setup that had no margin to spare.

Each row takes the momentum your arrow has left at that distance, adjusts it for the head and the FOC, and turns it into an estimated depth into that animal. The bar shows that depth against the animal's body; the upright line marks where the far side of the vitals sits on a broadside shot.

• Pass-through — modelled depth exceeds the full body width.
• Sufficient — reaches through the vitals but stops inside.
• Insufficient — falls short of the far side of the vitals, which is where wounding rather than killing starts.

The animal figures are averages for a mature broadside animal — roughly 15 in through a whitetail, 22 through an elk, 32 through a buffalo, with vitals sitting proportionally inside. Bigger and smaller individuals exist, and a quartering angle changes everything.

Check it: 450 gr at 280 fps with a three-blade head reads pass-through on deer at 40 yd and sufficient — but not through — on elk. That is very close to how that setup is usually described by people who hunt both.

ArcheryEra Penetration Score: a proprietary comparison model — not a laboratory penetration measurement. It's a single 0–100 read anchored on elk-class work, because that's where setups start to separate. 50 means the arrow just reaches the far side of elk vitals at the distance you've set. Above 50 you're into pass-through territory with progressively more in hand; below it you're short.

It is a comparison tool, not a grade, and not a published penetration standard. Use it to see whether swapping a head or adding 50 grains actually moved anything. Don't read 74 as meaningfully better than 71.

Penetration estimates rest on assumptions that a calculator has no way to check:

• The arrow is flying straight. A broadhead that planes because the arrow is out of tune loses more penetration than every setting on this page combined.
• Blades are sharp. A dull head is a different projectile.
• The shot is broadside and behind the shoulder. Heavy bone changes the picture entirely, and no momentum figure predicts what happens when an arrow meets a scapula.
• Average tissue. Real animals vary by season, age, condition and species within a class.
• Shaft diameter, single-bevel versus double-bevel grind, insert and footing construction, and how well the head is aligned with the shaft all matter and none of them are inputs here.

A well-placed arrow from a modest setup out-performs a badly placed one from an impressive setup, every single time. If a species is new to you, ask people who hunt it — and check your local regulations, which often set minimum draw weight or arrow weight regardless of what any calculator says.

• Speed: chronograph three arrows with the broadhead you'll actually hunt with, and average them. Everything on this page is downstream of that one number.
• Weight: weigh the finished arrow on a grain scale, complete — head, insert, wrap, vanes, nock. Not the shaft's advertised figure.
• FOC: balance the finished arrow on a straight edge and measure. It's a two-minute job and most people are surprised by the answer.
• Penetration: shoot layered cardboard or a dense foam block at your real hunting distance, then change one thing and shoot again. Relative results from your own bow beat any model's absolute numbers.

If your results disagree with this page, believe your results — and leave a comment below so the next reader gets the benefit.