Field Notes

How accurate is ArrowForge's FPS estimate? I tested it.

3 builds, a Garmin Xero, zero wind. Here's what the numbers say — and what we updated as a result.

David Marcus · June 2026

Every trajectory, kinetic energy, and sight pin calculation in ArrowForge starts from one number: your arrow's velocity. If you've shot through a chronograph, you can enter that exact reading. But if you haven't — which covers a lot of people — the app estimates FPS from your bow's IBO speed and a few setup parameters.

I wanted to know how good that estimate really was. Not "good enough for a spreadsheet" good — actually good. So I set up a controlled test and ran three of my builds through a Garmin Xero S1 chronograph.

How the estimate works

ArrowForge uses an ATA-derived formula — the same framework bow manufacturers use when they publish IBO ratings. You enter your bow's manufacturer-rated IBO speed, and the app adjusts from there:

The efficiency factor accounts for the gap between a perfectly controlled lab environment and a real bow in someone's hands. The IBO standard measures speed at 70 lbs, 30" draw, with a 350 gr arrow and nothing on the string. Most hunting setups deviate from all of those conditions.

Test conditions

I tested three builds — each one a real hunting build I've been shooting. Three shots per build at identical conditions. I used the average of all three shots as the reference speed.

Results

Two of three builds land within 2 fps of the actual reading. For a formula working entirely from published specs with no bow-specific tuning data, that's solid. The Hornet and Bonecrusher — both heavier arrows in the 515–548 gr range — came in within 2 fps. The Freight Train, with a 466 gr arrow, showed a larger gap.

One thing stands out across all three: every error is negative. The app consistently underestimates. That's actually the direction you want for a conservative tool — your real-world performance meets or exceeds the app's predictions, rather than falling short of them.

What we changed

The efficiency factor in the formula was set at 0.97 — meaning the formula assumed 3% energy loss versus the IBO lab condition. The chrono data implied the real-world efficiency was closer to 0.977–0.978 for the heavier builds.

We bumped the factor from 0.97 to 0.975. For the Hornet and Bonecrusher this closes the gap to under half an fps. The Freight Train improves too — from −5.5 fps to about −4.4 fps — but that residual gap reflects something the formula doesn't fully model yet.

The estimate is conservative by design. A few fps low is far better than a few fps high — it means your trajectory math and KE numbers are working with real-world margins, not optimistic ones.

Why the lightest build is harder to nail

The Freight Train's larger error likely reflects a real gap in the formula: the current model doesn't include a draw weight adjustment for compound bows. IBO speed is measured at 70 lbs — this bow runs at 80 lbs, which stores more energy. The formula's efficiency factor absorbs some of that difference, but not all of it.

Adding a draw-weight term is the logical next step. The data I have doesn't let me calibrate it — all three tests were shot at the same poundage. To isolate the draw-weight effect cleanly, I need chrono tests at a second draw weight on the same bow. That's on the list.

Limitations of this data

Three builds. One bow. One draw weight. One draw length. This is a calibration baseline, not a statistically robust study. The formula update improves accuracy for setups similar to this test: modern compound, 27–29" draw, 70–85 lb draw weight, heavier hunting arrows in the 480–560 gr range.

If your setup is meaningfully different — especially if you're shooting a lighter arrow under 450 gr, or a much higher or lower draw weight — I'd encourage you to shoot through a chrono and enter the measured number directly. ArrowForge's Live Settings panel accepts a chronograph reading and uses it as the authoritative FPS source instead of the estimate.

If you've run your own chrono tests and want to share the data, reach out. More data points at different draw weights and bow types will let us keep tightening this up.