A litre of oil is circa top to bottom marker on the dipstick.
If the oil level is low, it will get hotter than when operating at normal oil level, which causes higher oil consumption and thus it drops more quickly.
But as above need to establish if there is a leak? Did you check the level post service and was it ok? If so, then 1+ ltr in 2.5k miles is rather high.
Any pooling of oil, oil spray in the engine bay, blue or white smoke from the exhaust? Could be any number of things - Oil filter not secure post service, sump plug, oil cooler, faulty turbo.