Descent Rate Calculator
Planning a descent is simple arithmetic, but doing it in your head while flying is how pilots end up high and fast on final. Enter your altitudes, groundspeed, and whichever fact you already know, distance, rate, or time, and this tool solves for the rest, including the descent gradient, the descent angle, and how your plan compares to the textbook 3-degree profile.
The fourth mode covers the other kind of descent nobody plans: engine-out glide range from your best glide ratio and your height above terrain. Every result below is advisory, for flight planning practice and cross-checking, and never a substitute for your pilot operating handbook, current charts, or pilot in command judgment.
Quick Answer
Key takeaways
- Four modes solve the same descent triangle from whichever corner you know: required rate from distance, top of descent from a chosen rate, time in descent, and engine-out glide range.
- Every powered mode reports gradient in ft/NM and angle in degrees together, plus the glide ratio of the profile, so a plan can be cross-checked three ways at a glance.
- The 3-degree verdict compares your rate with groundspeed times 5, with a tolerance of 100 fpm either way before it calls a plan steep or shallow.
- The famous shortcut, start down 3 NM per 1,000 feet, is an approximation: at exactly 600 fpm and 120 knots, losing 10,000 feet actually takes 33.3 NM, not 30.0 NM. This tool does the exact division.
- Quick Answer
- How to use this descent planner: four modes, one triangle
- The formulas behind the numbers
- Worked example: 12,000 feet to 2,000 feet, 30 NM to run
- The same descent through the other three modes
- The 3-degree rule, and where the shortcut bends
- Typical descent rates, from the times-5 rule
- What competing calculators miss
- Frequently Asked Questions
- Add This Calculator to Your Website
- References
How to use this descent planner: four modes, one triangle
Pick the tab that matches what you know. The first three modes share the same altitude and groundspeed fields and differ only in which extra fact you supply and which answer is headlined.
Required rate answers "how fast must I come down?" Enter current and target altitudes, groundspeed, and the nautical miles available. Use it for crossing restrictions, where the distance is fixed and the rate has to fit it.
Top of descent answers "where do I start down?" Enter the comfortable rate you plan to fly, and the tool converts it into the distance out at which the descent must begin. If you are measuring the leg for the first time, the air distance calculator gives the direct distance between two points to plan against.
Time in descent answers "how long will I be going down?" It takes the same inputs as Top of descent and headlines the minutes instead of the miles, which is the number that matters for descent checks, passenger briefings, and fuel timing.
Glide range answers "how far can I glide from here?" It swaps the altitude fields for your best glide ratio and height above terrain, and returns still-air glide distance in nautical and statute miles with an estimated time to the ground.
The formulas behind the numbers
All four modes are the same triangle solved from different corners. Altitude to lose is always current altitude minus target altitude, and every other answer follows from time, distance, and groundspeed.
Gradient and angle describe the same slope in two dialects, the way a road's grade and its angle do, a relationship the average slope calculator explores for terrain. Controllers and procedure designers think in ft/NM; pilots picturing the flight path think in degrees. A gradient of about 318 ft/NM is exactly 3 degrees. In glide mode, the time to the ground is estimated at a fixed 70 knots, a typical best glide speed for a light single, which is a stated assumption of the tool rather than a value it takes from your handbook.
Worked example: 12,000 feet to 2,000 feet, 30 NM to run
You are cruising at 12,000 feet and need to be at 2,000 feet 30 nautical miles ahead, with a groundspeed of 120 knots. The Required rate tab is pre-filled with these four numbers, and this is exactly what it returns.
| Output | Result | How it is reached |
|---|---|---|
| Altitude to lose | 10,000 ft | 12,000 minus 2,000 |
| Time available | 15.0 min | 30 / 120 x 60 |
| Required descent rate | 667 fpm | 10,000 / 15.0, rounded to a whole number |
| Descent gradient | 333.3 ft/NM | 10,000 / 30 |
| Descent angle | 3.1 degrees | arctan(10,000 / (30 x 6,076.12)) |
| Glide ratio of this profile | 18.2:1 | (30 x 6,076.12) / 10,000 |
| 3-degree rule check | On a 3-degree profile | Textbook rate is 120 x 5 = 600 fpm from 30.0 NM out |
Read the verdict with its tolerance in mind. The check compares your rate against groundspeed times 5 and allows 100 fpm either side before calling a profile steep or shallow, which is why 667 fpm passes as on profile against a 600 fpm textbook figure. It is a reasonableness check, not a precision instrument.
The same descent through the other three modes
Keep the same 10,000 feet to lose at 120 knots and change only the question. At a planned 500 fpm, the descent needs more room than the 30 NM in the first example; at 1,000 fpm it fits easily but the verdict objects. The glide case is the pre-filled engine-out example.
| Mode | Extra input | Headline output | Gradient and angle | Verdict or note |
|---|---|---|---|---|
| Top of descent | 500 fpm planned rate | 40.0 NM needed | 250.0 ft/NM, 2.4 degrees | On a 3-degree profile, within the 100 fpm tolerance |
| Time in descent | 500 fpm planned rate | 20.0 min | 250.0 ft/NM, 2.4 degrees | Same plan, headlined in minutes over 40.0 NM |
| Top of descent | 1,000 fpm planned rate | 20.0 NM needed | 500.0 ft/NM, 4.7 degrees | Steeper than a 3-degree path: ideal is about 600 fpm |
| Glide range | 9:1 ratio, 5,000 ft AGL | 7.4 NM still-air glide | 9.0:1 glide ratio | 8.5 sm, 6.3 min to the ground at 70 kt, 45,000 ft of glide |
Treat the glide figure as the outer edge of your options, never as a promise. It assumes still air, a clean airplane at best glide speed, and a straight line to the landing spot. Headwind, turns, rain, and a windmilling propeller all shorten it, which is why experienced pilots plan to arrive over their chosen field with altitude in hand rather than on the geometric limit.
The 3-degree rule, and where the shortcut bends
The two cockpit shortcuts behind the verdict are worth memorizing on their own: start down 3 NM for every 1,000 feet to lose, and fly a rate equal to your groundspeed times 5. They encode the geometry of a 3-degree path, the same slope an ILS glideslope flies, and the FAA's Airplane Flying Handbook covers descent planning built on this profile. What the shortcuts hide is that they are rounded. Three miles per thousand feet implies a gradient of 333 ft/NM, slightly steeper than the true 3-degree gradient of about 318 ft/NM, and the times-5 rate rule is similarly approximate.
The difference is small but real, and this tool shows it. Losing 10,000 feet at exactly the textbook 600 fpm takes 16.7 minutes, which at 120 knots is 33.3 NM of travel, not the 30.0 NM the times-3 shortcut names. The shortcut gets you down a little steeper and a little sooner than a true 3-degree path, which is a safe direction for an error to lean, but when a crossing restriction is tight, run the exact numbers here rather than the rounded ones.
Wind reaches every one of these numbers through groundspeed. A tailwind in the descent stretches the ground you cover per minute, so the same rate needs more miles and an earlier top of descent; a headwind compresses the plan. The tool takes wind as already included in the groundspeed you enter, and the crosswind calculator breaks down what a reported wind is doing to your track and groundspeed on the way down. Re-run the numbers with the groundspeed the GPS actually shows once the descent is established.
Typical descent rates, from the times-5 rule
Because the textbook rate is just groundspeed times 5, typical descent rates scale directly with how fast the airplane travels over the ground. These are the rule's outputs at common descent groundspeeds, not aircraft limitations.
| Aircraft class | Typical descent groundspeed | 3-degree rate (groundspeed x 5) |
|---|---|---|
| Light trainer | 90 kt | 450 fpm |
| Light GA cruiser | 120 kt | 600 fpm |
| Turboprop | 250 kt | 1,250 fpm |
| Jet in descent | 300 kt | 1,500 fpm |
For comfort, small unpressurized airplanes typically descend at 500 to 700 fpm, while pressurized aircraft commonly use 1,000 to 1,800 fpm. If the required rate for your distance comes out far above the comfortable band for your airplane, the honest answer is that the descent was started late: add track miles, accept a vector, or slow down, rather than diving at the number.
What competing calculators miss
Most descent calculators do exactly one thing. The simple ones take altitude and time and return a rate, with no distance solving, no gradient, and no angle. Several top-of-descent tools hard-code the 3-degree rule, so they can only ever describe one profile and cannot test the rate you actually intend to fly. The strongest competitor matches this tool mode for mode on rate, distance, gradient, and glide range, but it never tells you outright whether your planned rate sits on the textbook profile, and it reports no time-to-ground estimate in glide mode.
This page adds the two readouts those tools leave out: an explicit steep, on-profile, or shallow verdict on every powered plan, with its tolerance stated in the open, and a dedicated glide mode that converts range into statute miles and minutes as well as nautical miles. It also shows its working when the famous shortcut and the exact math disagree, instead of presenting the rule of thumb as exact.
Frequently Asked Questions
Descent rate is the vertical speed at which an aircraft loses altitude, expressed in feet per minute (fpm). It is the number you set on the vertical speed indicator to arrive at a lower altitude at a chosen point. This calculator works it out from your altitudes, groundspeed, and the distance, rate, or time you already know.
Around 500 to 700 fpm keeps passengers comfortable and stays well within what most light airplanes can do. Pressurized aircraft typically descend at 1,000 to 1,800 fpm. Much above 1,000 fpm in a trainer usually means the descent was started too late, and the better fix is more track miles or an earlier top of descent rather than a steeper dive.
For a quick estimate, with the 3-degree rule: multiply the altitude to lose in thousands of feet by 3 to get nautical miles, so losing 6,000 feet means starting down about 18 NM out. For the exact figure, divide the altitude to lose by the rate you plan to fly to get minutes, then multiply by groundspeed. The Top of descent mode does that exact version: 10,000 feet at 500 fpm and 120 knots needs 40.0 NM.
Two cockpit shortcuts that describe the same profile: start down 3 NM for every 1,000 feet to lose, and fly a rate equal to your groundspeed times 5, which is 600 fpm at 120 knots. It matches the geometry of a standard ILS glideslope, whose true gradient is about 318 ft/NM. The shortcuts are rounded, so this tool also does the exact math and flags plans more than 100 fpm from the textbook rate.
Through your groundspeed, yes. A tailwind on the way down means more track miles covered for the same rate, so you start down earlier; a headwind compresses the plan. Enter the groundspeed you expect in the descent rather than your cruise groundspeed, and re-check the plan against the GPS groundspeed once the descent is established.
Gradient is feet lost per nautical mile travelled, in ft/NM; angle is the same slope expressed in degrees. A 318 ft/NM gradient equals a 3-degree angle, and the worked example on this page, 333.3 ft/NM, equals 3.1 degrees. This tool reports both for every powered plan because controllers plan in gradients and pilots picture angles.
Because they solve the same triangle and simply headline different answers. Both take your altitudes, groundspeed, and the rate you plan to fly; one leads with the distance needed, the other with the minutes the descent takes, and both fill in the combined time and distance readout. Pick whichever headline matches the question you are actually asking.
It divides the still-air glide distance by a fixed 70 knots, a typical best glide speed for a light single. From 5,000 feet AGL at a 9:1 glide ratio, that gives 7.4 NM of glide and about 6.3 minutes before reaching the ground. Your actual best glide speed comes from your pilot operating handbook, and wind, turns, and configuration will all shorten the real distance.
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References
- Federal Aviation Administration, Airplane Flying Handbook (FAA-H-8083-3C), chapter 16, "Descent Planning" and "Descent Energy Management" - the FAA's own treatment of planning descents in jet and transition aircraft, behind the 3-degree profile used throughout this article. FAA: Airplane Flying Handbook (FAA-H-8083-3C), full text PDF. Accessed October 2026.
- FlightDecide, "Descent and Glide Calculator" - the strongest competing tool checked for the competitor comparison, solving for rate, distance, and gradient with a glide mode, and citing the FAA handbooks. FlightDecide: Descent and Glide Calculator. Accessed October 2026.
- Pilot Institute, "How to Calculate Your Descent Profile" - flight school guidance on top of descent and rate of descent using the 3:1 rule and the groundspeed times 5 rate rule. Pilot Institute: How to Calculate Your Descent Profile. Accessed October 2026.
- North Star VFR, "How to Calculate Your Top of Descent" - a certificated flight instructor's walkthrough of the rule of thumb method and the exact vertical speed and groundspeed version. North Star VFR: How to Calculate Your Top of Descent. Accessed October 2026.
- Sage Calculator, "Top Of Descent Calculator" - a competing single-purpose top of descent tool checked for the competitor comparison in this article. Sage Calculator: Top Of Descent Calculator. Accessed October 2026.