Top Of Descent Distance
Calculator
Results
- Distance (NM)
- 97.222222
- Time (minutes)
- 13.888888
- Descent gradient (ft per NM)
- 257.142857
Aviation and marine results
| Distance (NM) | 97.222222 |
| Time (minutes) | 13.888888 |
| Descent gradient (ft per NM) | 257.142857 |
formula-map diagram
- Distance (NM)
- 97.222222
- Time (minutes)
- 13.888888
- Descent gradient (ft per NM)
- 257.142857
Aviation and marine relationship
Formula
TOD distance = GS × (altitude ÷ ROD) ÷ 60= 97.222222222222
Note
This is a simplified model: it applies a standard navigation, performance or seamanship formula to the numbers you entered. True airspeed and density altitude use the ISA troposphere model for dry air and ignore humidity, compressibility and instrument or position error, so they are not a substitute for your aircraft's flight manual or an air data computer. Wind, climb, descent and fuel figures assume a steady wind and a constant speed and fuel flow for the whole leg; they ignore manoeuvring, holding, taxi and start-up fuel, terrain, turbulence and air traffic control routing. Takeoff distance scales an entered sea level figure by a rule-of-thumb percentage per 1000 ft of density altitude and is not a certified performance chart. Weight and balance results depend entirely on the arms and weights you enter and must be checked against the approved loading envelope. Hull speed is the classic 1.34 × √LWL displacement estimate, boat fuel burn is a horsepower-based approximation, anchor scope is a rule of thumb, and the rule of twelfths is a linear approximation of a sinusoidal tide that does not hold in all locations. Always use official charts, tide tables, the aircraft or vessel manuals and current weather, and treat these numbers as planning estimates only.
More in Aviation and marine
See all →Frequently asked questions
What is top of descent (TOD) and why do pilots calculate it?+
Top of descent is the point along the route where an aircraft must begin descending from cruise altitude to arrive at a target altitude — usually at the destination or a fix — while following a planned descent angle or rate. Calculating it in advance helps avoid a rushed, steep descent late in the flight.
How is the top of descent distance calculated?+
A common rule of thumb is: distance (nautical miles) = altitude to lose (in thousands of feet) × 3, based on a standard 3° descent path. For a more precise result, the calculator uses your groundspeed, descent rate, and altitude to lose to compute the exact distance required.
Why does groundspeed matter for this calculation, not just descent rate?+
The distance covered during the descent depends on how fast you're moving over the ground while descending, not just how quickly you're losing altitude. A faster groundspeed during descent means you cover more distance for the same descent rate, so you need to start descending further out.
What's a common mistake when planning top of descent?+
Using a single descent rate for the entire descent when in reality groundspeed and often descent rate change as the aircraft slows and encounters different winds at different altitudes. Treating TOD as a single fixed point rather than continuously updating it in flight can lead to being high or low on profile.
Does wind affect where top of descent should be?+
Yes — descending into a headwind reduces groundspeed, which shortens the distance covered during descent, so TOD can start slightly later. Descending with a tailwind increases groundspeed and the distance covered, so you generally need to start descending earlier.