Enter your pellet's weight and caliber, then two or more chronograph readings at known distances. The calculator runs a real trajectory simulation against the standard G1 drag model and solves for the ballistic coefficient that matches your measured velocity loss, it doesn't use a shortcut formula. See Ballistic Coefficient and Sectional Density in the glossary for background on what BC actually measures.
Ballistic coefficient compares how well a pellet holds its velocity against a standard reference projectile shape. This calculator uses the G1 reference shape, one of the most widely used ballistic standards, tabulated from real drag testing conducted by the US Army Ballistics Research Laboratory under Robert L. McCoy, and published by JBM Ballistics.
Rather than plugging your numbers into a single formula, the calculator actually simulates your pellet's flight: it tries a ballistic coefficient, runs a real trajectory calculation against the G1 drag data at each point along the flight path, and checks whether the predicted velocity at your measured distance matches what your chronograph actually recorded. It repeats this, narrowing in on the BC value that best explains your real, measured velocity loss.
A single pair of readings can be noisy, chronographs have real-world measurement error, and any one pair of shots might not be representative. If you can chronograph at three or four distances instead of two, add each one with + Add Measurement. The calculator will find the single BC value that best fits all of your readings together, and tell you how good that fit actually is.
The G1 reference shape is a simple, flat-based bullet profile. That's a reasonably close match for airgun slugs, but classic waisted, skirted diabolo pellets have a meaningfully different aerodynamic shape. G1 still gives a usable estimate for diabolo pellets, it's what most published pellet BCs use, but treat it as a rougher approximation for diabolo shapes than for slugs specifically.
This calculator is free to embed anywhere, including WordPress, no plugin required. Paste the code below into a Custom HTML block (or anywhere in your page's HTML):
<iframe src="https://airgunguide.com/embed/airgun-bc-calculator.html" width="100%" height="900" style="max-width:420px;" title="Airgun Ballistic Coefficient Calculator"></iframe>
<script src="https://airgunguide.com/js/embed-listener.js"></script>The script after the iframe lets the calculator resize itself automatically as you add measurements, so it never shows an internal scrollbar. If you embed more than one AirgunGuide calculator on the same page, it's fine to paste this exact block for each one, no changes needed. In WordPress specifically: add a Custom HTML block to your page, paste the code above into it, and publish. That's it, no account, no API key, and no plugin needed.