FAR 121 calls for a 10% International Contingency Fuel from point A - B.
So, as an example, on a flight from SIN to LHR on a 747-400 with a trip fuel of say 144.0 tonnes, and reserves plus alternate of 7.6 you would have to take 14.4 tonnes of contingency and therefore Planned Remaining of 22.0 tonnes?
Cherist!
Todays BAxx from SIN was planned to depart with above numbers except with 95% statistical contingency of 3.6 tonnes, still planning to land with about 1.25 hours fuel remaining! 22 tonnes would equate to about 2.5 hours (and reduce payload by the same incremental fuel amount loaded [10.8 tonnes]).