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# Sectional Density

MichaelBartmess.Sectional Density

This **Sectional Density** calculator computes the factor used in the computation of the ballistic coefficient called sectional density

**INSTRUCTIONS:** Choose units and enter the following:

**(M)**- This is the mass of the projectile**(d)**- This is the diameter of the projectile

**Sectional Density (SD):** The value is returned as a real number

#### The Math / Science

The mass is converted to pounds and the diameter to inches. The formula for sectional density is

SD = M/d²

where:

- SD is the sectional density
- M is the mass of the projectile or bullet in pounds
- d is the diameter of the projectile or bullet in inches.

This calculator automatically converts grains, grams and other mass/weight units to pounds, and millimeters and other length units to inches. The resulting answer is provided with no units.

The sectional density as applied to a bullet is slightly different than the sectional density definition as applied in a general physics context. Sectional density in a general physics context is defined as mass per cross-sectional area. Sectional density is approximated as mass per diameter squared.

The ballistic sectional density is used to compute the ballistic coefficient (See equation: **Ballistic Coefficient**). The ballistic sectional density is also used in computation of the penetration characteristics of terminal ballistics.

#### Related Calculators

- Miller Twist Rule
- Ballistic Coefficient
- Greenhill Formula for Optimal Riffling Twist Rate
- Ballistic Range
- Muzzle Energy of a Projectile
- Recoil Velocity of a Gun

#### References

**Sectional Density**, is listed in 1 Collection.