Aviation & Aeronautics
Basic

True Airspeed (rule of thumb)

Quick estimate: true airspeed increases about 2% per 1000 ft of altitude above indicated airspeed.

Formula

TAS≈IAS+(IAS×0.02×alt1000)TAS \approx IAS + (IAS \times 0.02 \times \tfrac{alt}{1000})

Variables

TASTrue airspeed
IASIndicated airspeed
altAltitude (ft)

Example

IAS 100 kt at 5000 ft: TAS ≈ 100 + 100×0.02×5 = 110 kt

Did You Know?

True airspeed rises above indicated airspeed with altitude — roughly 2% per 1,000 feet as the air thins.

airspeedtasiasperformance