Takeoff calculations are not single-number figures. Calculations depend on multiple factors, including pressure altitude, temperature, weight, wind, runway slope, and climb gradient with an engine failure. The latter in turn depends on the runway to be used, considering surrounding terrain and obstacles, and performance based on the previous elements: pressure altitude, temperature, weight, and wind.

A takeoff is not simply calculated in terms of pavement used, but stopping distance (what are the surface conditions? Wet? Dry? Slick?), which includes conditions, runway type, etc. Brake temperature may also be factor. Additional factors apply to the specific aircraft and it's condition, operative or inoperative equipment (autospoilers, takeoff autobrakes, etc).

Also to be taken into consideration and calculated for each takeoff is center of gravity and trim setting.

Not only must the aircraft leave the ground, but must climb at a minimum gradient with an engine failed or not producing thrust. Every takeoff is calculated not just with takeoff distance, but accelerate-stop distance, accelerate-go distance, balanced field length (when accel-stop and accel-go are equal), taking into account all relevant factors, including obstacles or temporary obstacles, and any equipment changes that affect performance.

An aircraft can get off the ground when empty in a fairly short distance; a choice of flap settings must be made, which in turn affects speeds and distances; these speeds are also established relative to the effects of asymmetric thrust: can the aircraft maintain directional control with one (or more) engines inoperative? An aircraft can get off the ground at a slow speed and climb slowly and steeply, but there are safety margins to consider, which require faster climb speeds, longer distances, and shallower climb gradients.

Aircraft departing above their minimum landing weight will either have to accept a higher landing speed and longer distance on landing (and overweight landing) in the event of a required return in an emergency (eg, fire), or must dump fuel down to the landing weight.

Maximum weights vary with the serial number. Typically 287,124 kg for taxi, 285,990 kg for takeoff, 222,941 for landing. There are also maximum weights for inflight landing flaps (224,301 kg) and zero fuel weight (209,242 kg). The last weight is the maximum allowable weight of the aircraft before fuel is included; anything above that weight must be fuel.

In the case of the MD-11, you must also take into account whether the aircraft has "deflected ailerons" or not. These impact performance and configuration (flap setting), including takeoff distance. Some aircraft have deflected ailerons, which which the ailerons lower incrementally with the flaps to increase camber over a larger span of the wing, increasing lift. Some don't.

An airplane that's fairly light, 185,000 kg for example, at Los Angeles on a standard day could expect a reduced power takeoff with a takeoff distance required of approx 7,300'. The same aircraft, returning to land on the same no-wind runway, at the same weight, would need approximately 4300 for actual ground roll, an a landing distance of 7200' on a dry runway. On a wet runway those figures would increase to approximately 5000' and 8300' respectively, with a final approach speed of 150 kts.

Reduce those weights to 150,000 kg, with a 26% CG, and the takeoff number is approx 5000'. Landing at the same weight/CG/runway conditions yields approx 3700/6100 dry, and 4200/7000 wet. Those are ideal numbers; pilot technique can lengthen them. They're simply calculations. Change any of the factors and those numbers change, too.

Remember that each takeoff requires a full runway analysis that looks at the specific runway, and any obstacles or conditions particular to that runway at that moment, taking into account the other information specified. There is no one number that's used; it's calculated for every takeoff based on actual data, every time, and if a runway change is made or any changes are made with respect to configuration, weather changes, winds, center of gravity, and so forth, the runway analysis and performance calculations are re-done in entirety.