Descent Gradient Rate Calculator
Planning a descent comes down to two related questions: how steep the path is, and how fast you must come down in feet per minute to fly it. The gradient is set by the altitude to lose over the distance available, expressed as feet per nautical mile, a percentage, or an angle. The rate of descent then depends on ground speed, since covering the path faster means losing height faster. This calculator takes the altitude to lose, the distance, and your ground speed, and returns feet per nautical mile, the gradient percentage, the path angle, and the required rate of descent in feet per minute.
Descent gradient and rate formula
Feet per nm = altitude to lose / distance
Gradient % = (altitude to lose / (distance * 6076)) * 100
Path angle = arctan(altitude to lose / (distance * 6076))
Rate of descent = feet per nm * (ground speed / 60)
One nautical mile is 6,076 feet. Ground speed in knots divided by 60 gives miles per minute, so multiplying by feet per mile yields feet per minute.
Descent planning notes
- A 3 degree path is about 5.2 percent, near 318 feet per nautical mile.
- For a 3 degree path, ground speed in knots times 5 approximates the rate of descent in feet per minute.
- The gradient is fixed by geometry; the rate of descent scales with ground speed.
- To start a descent, divide the altitude to lose by the gradient in feet per mile to find the distance out.
- Wind changes ground speed, so recompute the rate of descent if the wind shifts.
Descent gradient: frequently asked questions
How do I work out the rate of descent for a given gradient?
First find feet per nautical mile by dividing the altitude to lose by the distance over which to lose it. Then multiply that by ground speed in knots divided by 60. The result is the required rate of descent in feet per minute, because ground speed in knots divided by 60 is miles per minute.
What is a descent gradient?
A descent gradient is the steepness of the descent path, often expressed as a percentage or in feet per nautical mile. As a percentage it is the height lost divided by the horizontal distance travelled, times 100. One nautical mile is 6,076 feet, which is used to convert between the two forms.
What is the three-degree rule of thumb?
A standard instrument approach descent path is about 3 degrees, which is close to a 5.2 percent gradient or roughly 318 feet per nautical mile. A common cockpit shortcut for a 3 degree path is to multiply ground speed in knots by 5 to get the approximate rate of descent in feet per minute.
Why does ground speed change the required rate of descent?
The gradient fixes how many feet you must lose per mile, but the rate of descent in feet per minute also depends on how many miles you cover each minute, which is ground speed. The faster you fly the path, the faster you must descend in feet per minute to stay on the same gradient.
How do I find the descent angle in degrees?
The descent angle is the inverse tangent of the height lost divided by the horizontal distance in the same units. This calculator converts the distance to feet using 6,076 feet per nautical mile, then takes the inverse tangent of altitude over distance to report the path angle in degrees.
Official sources
Reviewed by the CalculatorHub team, edited by James Graham, 17 June 2026. See our methodology.