Use this calculator to find the Incapacitation Index of any handgun cartridge. Incap Index is a metric built entirely on the real-world data described on the “Handgun Performance” page. The Stopping Power returned by the calculator is the projected Incap Index using the formula that mirrored the empirical data. Incap Index roughly corresponds to a 2-shot-stopping-power (based on some standard probability assumptions), but it’s built solely on real-world data instead. So far, known values for this measure of Stopping Power range from 44% for 25 ACP to 87% for 500 S&W.
Incapacitation Index Calculator
So what’s a “good” Incap Index value? I personally like values in the mid 60s (or higher); they roughly translate to a 2/3s chance of incapacitating with a couple of well-placed shots. Of course, there are a number of trade-offs in your “best-handgun-for-me” decision: your accuracy with a particular caliber or gun, ease of carry, handling qualities, etc. Incap Index is just one data point to help you in that calculus.
We can also assess the number of shots needed to reach a 90% probability of incapacitation … given the Incap Index value generated by the calculator above, and using some standard probability calculations and assumptions. Use this information with caution; the Incap Index calculation is solidly backed by real-world data, while the chart below relies on some necessary assumptions. But the chart does provide a related result that is sometimes more intuitively understood (though a very rough estimation). A few common calibers are marked on the chart.
