F111,
it depends on airspeed, of course. You have the option of normal or long range cruise. For a heavy aircraft:
10000 ft press. alt: 218-280 KTAS, 390-585 kg/h
15000: 223-284 KTAS, 355-529 kg/h
20000: 233-283 KTAS, 336-467 kg/h
No guarantee at all that I didn't get a number wrong somewhere.
Regards,
Fred