Typical tail clearance during takeoff is between 50 and 75 cm / 20 and 30 inches. This clearance increases with flap setting. Consider using Flaps 15 for takeoff with low gross weight.
Subtract about 2 degrees from the table values to get landing tail strike pitch (wings level - gear struts compressed).
Takeoff Tail Strike Pitch -800 : 11.0 degrees
Typical factors contributing to a tailstrike are :
On Takeoff
The loadsheet is handed-over to the crew at a moment of high workload on the flight deck. Always crosscheck all FMC weight and speed entries, takeoff performance computations and trim setting. Never expedite or skip proper weight and speed verifications in an attempt to make the flight schedule !
On Landing
There is nothing wrong with a go-around even if this go-around is due to an unstabilized approach. But there is definitely something wrong with a tailstrike or a runway overrun!
Post FLT
AMM 05-51 - Even if there is no apparent damage, each tail strike event requires maintenance inspection.
For more information, refer to
FCTM 3.x [Takeoff Tail Clearance]
FCTM 6.x [Body Clearance at Touchdown]
FCTM 8.x [Tail Strike]