The quality of coal comes into the calculation to how much is burnt per day. Heating values referred as Calorific Value.
Best coal was Welsh grade 1.However seen the national coal strike was in progress leading to a shortness of coal and ships laid up. One could not be too choosy here. As Newcastle, Scotch and America coal were a softer grade burning at a quicker rate. The following BTU rating.
Best Welsh coal 16,000
Average Newcastle coal 14,900
Average Derbyshire and Lancashire coal13,900
Average USA coal 14.300
Average Scotch coal 14,200.
What was loaded on the Titanic in Southampton could of well been a bit of mix bag.
25th March in Belfast 3,000 tons of Scotch coal loaded. On arrival on 4th April in Southampton how much was burnt? If 1880 tons was load from coaling barges and a further 4,427 tons robbed from other ships bring extra coal over from America. Ships under IMMC. St Louis, New York, Philadelphia, Oceanic and Majestic. which well been USA coal. Total now 6,307. But a further 415 tons were burnt whist in Southampton leaving on the 10 April with 5,892 tons about 11% down from max at 6,611 tons
If burning at 650 tons per day which I very much doubt and was a lower figure due to all boilers not been lite. With 5,892 tons on board that give her just over 9 days sailing. Well in. O though Mark quotes 343 tons at 16 knots seems to be a rather low figure for speed? Or is there more I have missed!