At what speed does a Boeing 737 take off?

A takeoff doesn't have "the takeoff speed", but rather a trio calculated flight by flight. V1 is the decision speed: once exceeded, the takeoff continues even if an engine fails, because there's no longer enough runway left to stop. VR is the rotation speed, the moment the pilot pulls back on the controls and the nose rises. V2 is the safe climb speed with one engine inoperative. On a Classic or NG family 737, those figures almost always fall within the range of 240-290 km/h (130-155 kn) indicated.

Weight rules above everything: a 737 departing half-empty on a short route can rotate fifteen or twenty knots below one taking off at maximum weight with fuel for five hours. Flap position also matters, because a more extended configuration generates more lift at a lower speed, at the cost of drag.

The environment completes the picture. At a high-altitude airport or on a hot day the air is less dense, so the wing needs more true airspeed to produce the same lift and the engines deliver less thrust. That's why a takeoff in Mexico City in summer clearly requires more runway and more groundspeed than the same aircraft on a cold morning at sea level. A headwind, on the other hand, provides free relative speed and shortens the run.

It's worth distinguishing between indicated airspeed, which is what the pitot tube measures and reflects the dynamic pressure the wing feels, and groundspeed. The former governs the aerodynamics and barely varies between equivalent takeoffs; the latter can be considerably higher at elevated airports, and it's what the landing gear has to withstand.