Jackstee, it all depends on the KW of the boiler to the rate of usage, and how long you run the boiler, what the outside temperature is, how much area you are heating and to what temperature.
If you say that you only use 5 bags for a month, each bag must last 6 days that's just over 3kg a day, I would be very happy if my consumption was similar, that would equate to 3tl a day.
I run my 40kw boiler from 4-30 till 10-30, which heats every room in a 3 bedroom villa. Depending on the outside temperature I was using up to 20kg of supercarbon a night. Though the weather has not as yet got cold enough to establish how well the briquettes are going to perform, the indication is that the usage will be similar to the supercarbon, that would mean approx 20kg a day at roughly 12tl.
Hopes this answers your question.