Bullet Trajectory Calculator
Calculate bullet trajectory angle, estimated muzzle distance, and bullet drop from entry/exit hole positions and distance between surfaces.
About this calculator
Shooting reconstruction relies on the geometry of entry and exit points to work out where a shot came from. This calculator finds the trajectory angle by taking the arctangent of the height difference between the entry and exit points divided by the horizontal distance between the two surfaces — a positive angle means the bullet was traveling downward, negative means upward, and near-zero means a flat, roughly level shot. It separately estimates bullet drop — how far gravity pulled the projectile down over that same measured distance — using the physics of external ballistics, matching your entered caliber to one of six reference muzzle velocities (from a 9mm's roughly 370 m/s up to a .223/5.56's roughly 940 m/s) and applying the standard drop formula, drop = g·d² / (2v²), a good approximation only for the relatively short, flat trajectories typical of indoor or close-range shooting scenes where air resistance and bullet-specific ballistic coefficients matter less.
Note that the "estimated muzzle distance" output in this version is a placeholder scaling of the input distance rather than a fully derived ballistic solution — it should not be relied on for case work. This tool is meant for quick geometric sanity-checking of a trajectory rod or laser-line reconstruction, not as a replacement for full crime-scene photogrammetry: real reconstructions account for bullet deflection through intermediate materials, yaw, and the actual measured ballistic coefficient of the specific round involved, all of which this simplified two-point model ignores.
Inputs
Results
Trajectory Angle
2.39°
How to Use This Calculator
- Enter Entry Hole Height, Exit Hole Height, and Distance Between Surfaces.
- Set Bullet Caliber.
- Review the Trajectory Angle (°) result.
- Use Est. Muzzle Distance (ft) and Bullet Drop (in) to inform your decision.
- Use the chart to visualize the results and explore different scenarios by adjusting inputs.
How the result changes with Entry Hole Height
| Entry Hole Height | Trajectory Angle |
|---|---|
| 2.75 | -10.62° |
| 4.13 | -4.15° |
| 8.25 | 15.15° |
| 14 | 36.87° |
What each input means
- Entry Hole Height
- Height of the bullet entry point from the floor.
- Exit Hole Height
- Height of the bullet exit point from the floor (or impact on opposite surface).
- Distance Between Surfaces
- Horizontal distance between the entry and exit surfaces.
- Bullet Caliber
- Bullet diameter in mm (e.g., 9mm, 5.56mm, 7.62mm).
What each result means
- Trajectory Angle
- Downward angle of the bullet path (positive = downward, negative = upward).
- Est. Muzzle Distance
- Rough estimate of distance from muzzle to entry point.
- Bullet Drop
- Gravitational bullet drop over the measured distance.
How this is calculated
Worked example, using the default values
- Identify Input Parameters4 parametersEntry Hole Height = 5.5, Exit Hole Height = 5, Distance Between Surfaces = 12, Bullet Caliber = 9 = 4 input(s) provided
- Calculate Trajectory AngleTrajectory Angle2.39 = 2.39
- Calculate Est. Muzzle DistanceEst. Muzzle Distance12.6 = 12.6
Engine last updated . Checked against 2 independently-derived tests — how we verify calculators. Built by Paul Gunder, a software engineer, not a licensed financial, medical, or legal professional.
Frequently Asked Questions
How does the calculator pick a muzzle velocity from the caliber I enter?
It maintains a lookup table of typical muzzle velocities for six common calibers (5.56mm at 940 m/s, 7.62mm at 850 m/s, 9mm at 370 m/s, 10mm at 340 m/s, .45 ACP/11.43mm at 260 m/s, and .50 BMG/12.7mm at 900 m/s), then finds whichever reference caliber is numerically closest to your entered value and uses its velocity. If you enter a caliber that doesn't closely match any of the six, the estimate borrows the nearest one's velocity rather than interpolating, which can introduce error for calibers that fall between two very different reference rounds.
Is the 'Est. Muzzle Distance' output a real ballistic calculation?
No — as the explainer notes, this output is currently a simplified placeholder that scales the entered distance between surfaces by 1.05 rather than a fully derived solution from trajectory angle, bullet drop, and ballistic coefficient. It should be treated as a rough sanity-check number only, not relied on for actual case reconstruction.
What does a positive vs. negative trajectory angle mean?
The calculator computes the angle as the arctangent of (entry height minus exit height) divided by the horizontal distance between the two surfaces. A positive angle means the entry point was higher than the exit point, indicating the bullet traveled downward; a negative angle means the exit point was higher, indicating an upward path; and an angle near zero indicates a flat, level shot.
Why does bullet drop use gravity and velocity but ignore air resistance?
The drop formula used here, drop = g·d² / (2v²), is the basic physics of a projectile falling under constant gravitational acceleration over a fixed horizontal distance, without accounting for aerodynamic drag or the bullet's specific ballistic coefficient. The explainer notes this is a reasonable approximation only for the short, flat trajectories typical of indoor or close-range scenes — over longer distances, ignoring air resistance would understate the actual drop.
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