Sectional Density Calculator
Sectional density from bullet weight and diameter.
How this works
Sectional density describes how a bullet's weight is distributed relative to its frontal area — a long, narrow, heavy-for-caliber bullet has a higher sectional density than a short, light one of the same diameter. The 7,000 constant simply converts grains to pounds inside the formula.
Sectional density vs. ballistic coefficient
Sectional density is one of the two ingredients in ballistic coefficient (the other being the bullet's shape, or form factor) — see the Ballistic Coefficient Estimator to combine them. On its own, sectional density is most useful as a rough, caliber-independent way to compare how "heavy for its size" different bullets are before they hit anything.
Frequently asked questions
What's considered a "good" sectional density for big game?
There's no single universal number, but many hunters look for an SD of roughly 0.250 or higher for larger, tougher game, since higher SD is associated with deeper, more reliable penetration.
Does sectional density change if I switch bullets in the same caliber?
Yes — SD depends on both weight and diameter, so a heavier bullet in the same caliber will always have a higher sectional density than a lighter one, even though the diameter (and therefore the frontal area) stays the same.
Is sectional density the same as ballistic coefficient?
No — sectional density is one of the two ingredients in ballistic coefficient, the other being the bullet's shape (form factor). A high-SD bullet with a poor shape can still have a mediocre BC.
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