Calculator
Example data table
Values below are illustrative. Results depend on time-of-flight.
| Latitude (deg) | Azimuth (deg) | Elevation (deg) | Speed (m/s) | Time (s) | Cross-track drift (m) | Vertical drift (m) |
|---|---|---|---|---|---|---|
| 45 | 90 | 0 | 800 | 1.20 | ~0.07 | ~0.06 |
| 30 | 0 | 3 | 900 | 1.60 | ~0.00 | ~0.21 |
| -35 | 270 | 0 | 820 | 1.40 | ~0.07 | ~-0.07 |
Formula used
In a rotating Earth frame, the Coriolis acceleration is a = -2 (Ω × v), where Ω is Earth’s rotation vector and v is the projectile velocity.
Using local coordinates East–North–Up (ENU) and latitude φ, we model Ω = (0, Ω cosφ, Ω sinφ). With azimuth A (clockwise from North) and elevation θ, the initial velocity components are:
- vE = v cosθ sinA
- vN = v cosθ cosA
- vU = v sinθ
This calculator applies a constant-velocity approximation to estimate deflection over time-of-flight t: d ≈ ½ a t². That yields East, North, and Up offsets, plus cross-track drift (right is positive) relative to the shot azimuth.
How to use this calculator
- Enter your latitude, shot azimuth, and elevation angle.
- Enter muzzle speed and pick its unit.
- Choose a time-of-flight method: measured time or range-based estimate.
- Select an output unit for deflections (meters, inches, etc.).
- Press Calculate to view results above the form.
- Use the download buttons to export CSV or PDF reports.
Coriolis shooting correction notes
1) Rotation-driven drift
In a rotating Earth frame, a moving projectile experiences an apparent sideways acceleration that slightly bends its path. The effect is small at short distances, but it compounds with time of flight and can be measurable when you are chasing tight groups.
2) Inputs that set the geometry
Latitude determines how Earth’s spin axis is oriented relative to your local horizon. Shot azimuth and elevation split velocity into east–west, north–south, and vertical components, which controls both the sign and size of drift. Enter latitude with the correct hemisphere so the sign stays consistent.
3) Core equation used
The model uses ac = 2Ω(v × ŝ), where Ω ≈ 7.292115×10−5 rad/s and ŝ represents the rotation-axis direction. With a constant-speed approximation, integrating acceleration over time provides cross-range and vertical deflection estimates.
4) Why time of flight is central
Because the acceleration acts continuously, longer flight times accumulate more displacement. If you can supply a measured or validated time of flight, the correction is usually more dependable than a range-only estimate. When you only know range, use the estimate to bound the effect and revisit it after you confirm real flight time.
5) Expected magnitudes
For about 1.0 s of flight, lateral deflection is often millimeters to centimeters, depending on direction and latitude. At 2–3 s, it can reach several centimeters or more, especially for near east–west shots at mid to high latitudes. Outputs are provided in your selected unit for easy dialing and logging.
6) Directional behavior
East–west shots commonly show stronger cross-range behavior, while north–south shots can shift differently as the velocity aligns closer to the spin axis. Drift sign flips with azimuth changes and also differs between hemispheres.
7) How to apply results
Treat the cross-range output like a windage-style correction and the vertical output as a small add-on to your drop solution. Keep your sign convention consistent with your scope or aiming system before you commit adjustments. Save the inputs with your result so the correction is repeatable on similar stages.
8) Limits and best practice
This calculator isolates rotation-only effects and does not replace a full ballistic model with drag, wind, and spin drift. Use it to quantify Coriolis contribution, then validate with impacts and refine your overall dope. For critical shots, combine it with verified ballistic data and careful wind calls.
FAQs
1) Which direction does the drift go?
It depends on latitude, azimuth, and your sign convention. Use the reported signed cross-range and vertical outputs to decide whether to hold or dial left/right and up/down for your setup.
2) Should I enter true azimuth or magnetic azimuth?
Prefer true azimuth. If you only have magnetic, apply your local declination to convert to true north so the direction matches map and GPS bearings.
3) What time-of-flight option is best?
Measured time is best because Coriolis accumulates over time. The range-based estimate is useful for planning, but it can be off if drag, wind, or elevation changes alter the real flight time.
4) Does elevation angle change the result?
Yes. Elevation changes the velocity components and the angle to Earth’s rotation axis, shifting how the effect splits between cross-range and vertical deflection.
5) Is Coriolis the same as spin drift?
No. Spin drift comes from projectile spin and aerodynamics. Coriolis comes from Earth’s rotation. Add them together using a consistent sign convention.
6) What latitude format should I use?
Enter degrees as a decimal. Use positive values for the northern hemisphere and negative values for the southern hemisphere to keep the sign of the correction consistent.
7) When is this correction most important?
It matters most for long time of flight, precise targets, and mid-to-high latitudes. For short shots, wind and setup error often dominate, so Coriolis may be negligible.
Measure drift, adjust aim, and document every calculation clearly.