Coriolis Effect Calculator
Enter the mass, speed, latitude, and travel time of a moving object to compute the Coriolis force, acceleration, and deflection it experiences due to Earth's rotation. The result updates instantly as you type. Switch between metric and imperial units, and choose your hemisphere to see whether deflection goes left or right.
Formula
Worked example
A 1000 kg drone flying at 100 m/s at latitude 45 deg N for 3600 s (1 hour): |sin(45 deg)| = 0.7071, a = 2 * 100 * 7.2921e-5 * 0.7071 = 0.01031 m/s^2, F = 1000 * 0.01031 = 10.31 N, deflection = 0.5 * 0.01031 * 3600^2 = 66,834 m (~66.8 km to the right in the Northern hemisphere).
What is the Coriolis effect?
The Coriolis effect is an apparent deflection experienced by objects moving freely on or near Earth's rotating surface. It is not a real force in the Newtonian sense; it is a consequence of observing motion from within a rotating reference frame. In the Northern hemisphere, moving objects deflect to the right of their direction of travel. In the Southern hemisphere they deflect to the left. The Coriolis effect governs the rotation of large weather systems (cyclones spin counterclockwise in the north and clockwise in the south), ocean gyres, long-range ballistic trajectories, and even the path of air masses over continents. It has zero effect at the equator and reaches its maximum at the poles.
The Coriolis force formula
The magnitude of the horizontal Coriolis force is F = 2 * m * v * Omega * |sin(phi)|, where m is the mass of the moving object (kg), v is its horizontal speed (m/s), Omega is Earth's angular velocity (7.2921 x 10^-5 rad/s), and phi is the geographic latitude. The vertical bars indicate the absolute value of the sine, so the formula gives the same magnitude for a given latitude in either hemisphere. The corresponding Coriolis acceleration is a = F/m = 2 * v * Omega * |sin(phi)|. The deflection distance accumulated over time t is d = 0.5 * a * t^2. The factor of 2 in the formula arises from the cross-product form of the Coriolis acceleration (a = -2 Omega x v) when the rotation vector is projected onto the local vertical.
Why the Coriolis effect matters in practice
Even though the Coriolis acceleration is tiny compared with gravity, it becomes significant whenever an object travels far or fast enough. A long-range artillery shell fired 40 km will be deflected several hundred metres without correction. Transcontinental aircraft need continuous autopilot adjustment to hold a straight course. Ocean currents and wind patterns owe their large-scale organisation entirely to the Coriolis effect. At weather-system scales the deflection drives the characteristic spiral of hurricanes and typhoons. By contrast, the effect is negligible for water draining from a bathtub or sink: at that scale surface tension, basin geometry, and the initial swirl you gave the water when filling it completely dominate. The Coriolis effect only becomes meaningful over distances of tens of kilometres or time spans of many hours.
How to use this calculator
Enter the mass and horizontal velocity of the object in your chosen unit system (metric or imperial), the latitude of the location, the hemisphere (which determines deflection direction), and the duration of travel. The calculator instantly returns the Coriolis force in newtons, the Coriolis acceleration in m/s^2, the total lateral deflection distance in metres, the latitude factor |sin(lat)|, and the direction of deflection relative to the direction of travel. The step-by-step panel shows every stage of the calculation with your actual numbers substituted in. The deflection-vs-time chart shows how the lateral displacement grows as a quadratic function of travel time. Switch the unit system at any time and all values update immediately.
Latitude factor |sin(lat)| at key latitudes
| Latitude | Representative location | |sin(lat)| | Relative strength |
|---|---|---|---|
| 0 deg | Equator | 0.0000 | Zero - no horizontal effect |
| 15 deg | Tropics (e.g., Mumbai) | 0.2588 | Weak (~26% of maximum) |
| 30 deg | Subtropics (e.g., Cairo) | 0.5000 | Half of maximum |
| 45 deg | Mid-latitudes (e.g., Rome) | 0.7071 | Moderate-strong (~71%) |
| 60 deg | High latitudes (e.g., Oslo) | 0.8660 | Strong (~87%) |
| 75 deg | Sub-polar (e.g., Murmansk) | 0.9659 | Very strong (~97%) |
| 90 deg | Poles | 1.0000 | Maximum |
The Coriolis effect scales with the sine of latitude. At the equator it is zero; at the poles it is maximum.
Frequently asked questions
Why is the Coriolis force zero at the equator?
The formula contains the term |sin(latitude)|. At the equator, latitude = 0 deg, and sin(0 deg) = 0, so the horizontal Coriolis force is exactly zero. Earth's rotation axis is perpendicular to the local vertical at the equator, so there is no component of rotation that can deflect horizontal motion sideways. The vertical Coriolis effect (which slightly modifies the apparent weight of a falling object) does remain nonzero at the equator, but that vertical component is much smaller and usually ignored.
Why does the formula include a factor of 2?
The full Coriolis acceleration vector is a = -2 * Omega x v, a cross product of the angular velocity vector and the velocity vector. When you project Earth's angular velocity vector onto the local vertical at a given latitude you get Omega * sin(lat). Combining this with the magnitude |v| in a cross product gives the scalar expression a = 2 * v * Omega * |sin(lat)|. The factor of 2 is therefore an exact result of the vector mathematics, not an approximation.
Does the Coriolis effect cause water to spiral down a drain differently in each hemisphere?
In theory, yes, but in practice no. A bathtub or sink is far too small, and the water takes far too short a time to drain, for the Coriolis acceleration (roughly 10^-5 m/s^2 at mid-latitudes) to win out over the initial conditions you set when filling the basin, irregularities in the drain, and surface tension. Demonstrations that claim to show opposite spiralling in each hemisphere are carefully staged with symmetric basins left to settle for many hours. Natural large-scale systems such as hurricanes and ocean gyres are governed by the Coriolis effect because their scale and timescale allow it to dominate.
How do I convert the deflection from metres to kilometres or miles?
Divide metres by 1000 to get kilometres, or divide metres by 1609.34 to get miles. For example, a deflection of 66,834 m is approximately 66.8 km or 41.5 mi. The chart in this calculator plots deflection in metres on the vertical axis against time in hours on the horizontal axis.
How does the Coriolis effect influence weather and ocean circulation?
At the scale of weather systems and ocean basins, the Coriolis effect is one of the dominant forces shaping motion. It causes winds that would otherwise blow straight from high to low pressure to curve, producing the rotating structure of cyclones and anticyclones. Jet streams are steered partly by the Coriolis effect. In the oceans it drives the large circular gyres visible in every ocean basin and contributes to upwelling along coastlines. At these scales the Rossby number (the ratio of inertial to Coriolis forces) is small, meaning the Coriolis effect cannot be neglected.