Climb gradient and rate calculator
Rate of climb is feet per minute, which is what the instrument shows. Climb gradient is height gained per distance covered, which is what obstacle clearance depends on. Wind changes one without touching the other.
Calculator
This is an educational and planning aid. Use current official weather, your aircraft flight manual, and the rules that apply to your flight before you act on any figure here. See the aviation disclaimer.
What the result means
The gradient in percent is the height gained as a fraction of the ground distance travelled. A 5 percent gradient means 5 ft up for every 100 ft along.
Feet per nautical mile is the same thing in the units used on departure procedures and obstacle charts. Many published procedures require at least 200 ft per NM, which is 3.3 percent.
The angle in degrees is given for completeness. Climb angles are small: even a steep 10 percent gradient is under 6 degrees.
When this is useful
- Checking whether your aircraft can meet a published departure gradient on the day.
- Understanding why a departure that works into wind may not work downwind.
- Converting between the rate your aircraft achieves and the gradient a procedure demands.
How it is calculated
Groundspeed is converted into feet per minute of horizontal travel, then the rate of climb is divided by it. That ratio is the gradient, which is expressed as a percentage, as feet per nautical mile, and as an angle.
Because groundspeed is used, a headwind steepens the gradient for the same rate of climb, and a tailwind flattens it.
gradient (ft per NM) = rate of climb x 60 / groundspeed
Worked example
- Groundspeed
- 90 kt
- Rate of climb
- 700 ft per minute
The gradient is 7.7 percent, or about 467 ft per nautical mile, which is a climb angle of 4.4 degrees.
Check: 700 ft per minute multiplied by 60 minutes, divided by 90 kt, gives 466.7 ft per NM. Dividing that by 6,076 ft in a nautical mile gives 0.0768, which is the 7.68 percent shown. The two routes to the answer agree.
Limitations
- A published departure gradient is a minimum requirement set by obstacles. Meeting it in this calculator does not mean your aircraft will achieve it on a hot day at weight.
- It uses one steady rate of climb and groundspeed. Real climbs slow down as altitude increases.
- It describes geometry only, with no allowance for the acceleration and configuration changes in a real departure.
Common mistakes
- Using true airspeed instead of groundspeed. Gradient is measured against the ground, so the wind must be included.
- Confusing percent with degrees. A 5 percent gradient is about 2.9 degrees, not 5.
- Assuming a gradient met at sea level will be met at a high, hot airfield.
Sources
- Instrument Procedures Handbook (FAA-H-8083-16), departures , US Federal Aviation Administration