✈️ Useful Aviation Formulas Every Pilot Should Know

When you're flying, quick access to the right formulas can make a big difference—whether you're calculating descent rates, converting wind components, or planning fuel burn. Here's a collection of the most practical and frequently-used flight formulas, explained in a way that's easy to remember and apply. Bookmark this page as your go-to reference! Note that many of these formulas yield a workable approximation of the actual results.

1. Convert Climb Gradient (ft/NM) to FPM

Formula: Ft/NM requirement × NM per minute = FPM

Example: A departure procedure requires 300 ft/NM climb. At 120 KT ground speed

120 ÷ 60 = 2 NM/min So: 300 × 2 = 600 FPM

2. Descent Rate Formula

Formula: (Altitude to lose ÷ Distance to descend) × (Groundspeed ÷ 60) = FPM

Example: You need to descend 6,000 feet over 20 NM. Groundspeed = 120 KT

(6,000 ÷ 20) × (120 ÷ 60) = 300 × 2 = 600 FPM

3. calculate pressure altitude

Formula: (29.92 - Altimeter Setting) × 1,000 + Field Elevation

Example: Altimeter = 30.12 Field Elevation = 500' MSL

(29.92 - 30.12) × 1,000 + 500 = -200 + 500 = 300 feet

Tip: You can also set your altimeter to 29.92 to read pressure altitude directly. Just be sure to set it back to the correct reading!

4. Density Altitude Estimate

Formula: Pressure Altitude + [120 × (OAT - Standard Temp)]

Example: PA = 5,000 ft, OAT = 30°C Standard at 5,000 = 15 - (5 × 2) = 5°

5,000 + [120 × (30 - 5)] = 8,000 ft

5. Convert Indicated airspeed to True Airspeed

Formula: IAS + (IAS × 2% per 1,000 ft of pressure altitude) = TAS

Example: IAS = 120 KT at 8,000 feet pressure altitude

120 + (120 × [.020 × 8]) = 120 + 120 × 0.16 = 139 KTAS

6. Top of Descent (TOD) Distance

Formula: Altitude to lose in thousands of feet × 3 = TOD in NM

(Assumes a 3° descent angle - headwind or tailwind will require faster or slower rate)

Example: From 9,000 ft to 1,000

8,000 × 3 = 24 NM before destination

TIp: add three miles to this to arrive at bottom of descent prior to target such as traffic pattern

8. Ground Speed from Time and Distance

Formula: Distance ÷ Time = Groundspeed

Example: Covering 45 NM in 0.5 hours

45 ÷ 0.5 = 90 KT ground speed

9. Rate of descent to track glideslope

Formula: (Groundspeed × 10) ÷ 2

Example: Groundspeed = 90

(90 × 10) ÷ 2 = 450 feet per minute

OR: use groundspeed and multiply by 5

✈️ Bonus Tip: How to Convert Knots to MPH

Formula: Knots × 1.15 = MPH

Example: 100 KT = 115 MPH

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These formulas aren't just for checkrides—they’re tools working pilots use every day. Have a favorite formula you’d like to see added? Let us know!