Speed to fly (S.T.F.) is a technique used by soaring pilots when transiting between natural sources of lift, which includes thermal, ridge and wave.

The idea is to minimize the amount of time spent in the sinking air that is always found in between the rising air of the natural lift.

The minimal instrumentation required is an airspeed indicator and a variometer. The pilot will use the polar information for the particular aircraft. to derive the exact speeds to fly depending on the lift and sink conditions that the aircraft is flying in. These speeds must be memorized for various combinations of lift and sink.

The next step up in instrumentation is a speed to fly ring which is fitted around the aircraft's variometer, which is an instrument that indicates the amount of lift or sink the aircraft is experiencing, usually calibrated in either knots or meters per second. The ring will be designed based on the aircraft's polar. The pilot sets the ring's pointer opposite the expected climb rate and it then indicates various speeds to fly for sinking air at different sink rates.

The most technically advanced way to implement S.T.F. is through the use of a glide computer or equivalent software (commonly running on a PDA). The computer is connected to sensors that detect the aircraft's airspeed and sinkrate.

The glide computer or software can also calculate the speed and altitude necessary for a final glide for a particular destination. A final glide is where the aircraft can fly at a speed and rate of descent starting from a particular altitude, and reach the destination at a specified altitude, usually 1000 ft a.g.l. (above ground level).