Coal Bunker Capacities

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Sizes and Capacities

Choosing a Coal Bunker should be simple and straightforward, but can sometimes be more complex than you think. This guide explains how Coal Bunker capacities are measured, suggests capacities dependent upon application, and summarises which solid fuels are suitable for bunker storage and which aren’t.

When a bag of Coal isn’t a Bag of Coal

Historically, many Coal Bunker manufacturers have used the term ‘Bag of Coal’ or simply ‘Bags’  to describe the storage capacity of their bunkers. The terminology dates from a time when almost every bag of coal weighed a hundredweight (1 cwt) or there abouts, equivalent to approximately 50kgs today. So unsurprisingly a 3cwt bunker was known simply as a ‘3 bag’, a 6cwt bunker was a ‘6 bag’ and a 12cwt bunker was a ‘12 bag’.

However, in the intervening years, as well as a switch away from Imperial measures to metric, bags of coal have also got smaller. Whilst home delivered coal is often still sold in 50kgs capacity bags, a typical bag at a wholesale fuel supplier today might weigh 25kgs or even as little as 20kgs. Some pre-pack bags on forecourt sites can even weigh as little as 10kgs. So a ‘3 bag’ Coal Bunker, could accommodate as many as fifteen 10kgs bags of coal purchased from a forecourt site. And a ‘12 bag’ Coal Bunker could actually hold twenty-four 25kgs bags of coal purchased from a wholesale fuel supplier.

Despite the move towards smaller bags of fuel, the terminology used to describe Coal Bunkers has largely remain unchanged. Confusing, isn’t it? To overcome the confusion, we think it best to label Coal Bunkers by the approximate weight of Group 2 Household Coal they can store in kilograms (kgs), rather than by the number of bags of they can hold:

Table 1 Coal Bunker Capacity




50kgs Bags

25kgs Bags

20kgs Bags

10kgs Bags

3 Bag



3 Bags

6 Bags

7.5 Bags

15 Bags

6 Bag



6 Bags

12 Bags

15 Bags

30 Bags

10 Bag

10 cwt


10 Bags

20 Bags

25 Bags

50 Bags

12 Bag



12 Bags

24 Bags

30 Bags

60 Bags

Fuel Density

Just as not all bags of coal are created equal, neither are all coals. Some have a greater density than others, whilst some have a lesser density. So, if your preferred coal has a higher density than Group 2 Household Coal, you’ll be able to get more into your bunker. And if it’s less dense, you’ll be able to fit in less. Your Solid Fuel supplier can advise the relative density of different coal and fuel types.

Suggested Capacities

The easiest way to determine how much storage you require is to monitor how much fuel you use each week and decide how many weeks’ supply you wish to store. However, if you’re new to solid fuel,  then you may wish to refer instead to the guidelines below:

150kgs  Single Fire or Stove

300kgs  Small, Solid Fuel Central Heating System or up to 3 Fires / Stoves

600kgs  Large Solid Fuel Central Heating System

More than just Coal Bunkers

Whereas once the terms ‘Solid Fuel’ and ‘Coal’ were interchangeable, today there is probably a wider choice of solid fuels than ever before. Whilst most are suitable for bunker storage, Kiln Dried Logs, Wood Pellets and Wood Chips should always be stored in specialist containers.

And as as well as storing solid fuel, Coal Bunkers have a wide range of other applications too... storing anything from wellie boots to animal feed and almost anything in-between.

Queries? Questions?

If you require further guidance or assistance on choosing the ideal Coal Bunker, you’re very welcome to get in touch with us. You can call us on 01789 632 151 in the UK, Channel Islands and Isle of Man, 01 5268 642 in the Republic of Ireland or e-mail We’re open from 9am to 5pm weekdays - excluding Bank and Public Holidays.

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