NAPOLEON Blackstone Premium Lumpwood BBQ CHARCOAL 7KG (7 bags Gets you free delivery)

That's a really hard one to answer because it will depending on a number of factors, like what you're cooking, at what temp, and for how long and in what type of BBQ.

For example, a kamado ceramic BBQ is good as absorbing heat, so tends to burn charcoal more efficiently than standard ones. If you're searing steaks and want loads of heat, that obviously will eat through it faster than if you're just grilling some sausages, or if you're doing a 6-12 or even 24 hour lo-slo, that will burn through a lot.

To give you some idea, I bought a 12KG bag Big K charcoal in early June, and I've been cooking a couple of times a week on average, mostly just quick grill stuff, with the odd 6-8hr lo-slow, and I've about 1/6th of the bag left. I have a Kamado Joe Jr, and I reuse any left over charcoal from the previous cook. Sorry, not much help but truthfully the best way to work it out, is to buy a bag and see how you go. (edited)

My mate has for his Masterbuilt as well, as it is is recommended for lo&slo and high temp sears also.