What’s the Difference Between a Builder’s Bag and a Cubic Metre of Firewood?

When buying firewood, it’s easy to get confused between a builder’s bag and a cubic metre. Although both are common ways to sell firewood in the UK, they’re very different in terms of volume, weight and value. This guide explains everything you need to know so you can buy with confidence—and make sure you’re getting what you pay for.

1. What Is a Cubic Metre of Firewood?

A cubic metre (often referred to as a stere in the firewood industry) is a volume measurement of 1 metre × 1 metre × 1 metre. It’s widely accepted as the standard way of selling bulk firewood across the UK.

However, it’s important to understand the difference between stacked and loose firewood. When logs are loosely thrown into a cubic metre container, they take up more space than when neatly stacked. This means that a cubic metre of loose logs, when properly stacked, may compress to around 0.6–0.7 cubic metres in solid volume.

Also, the type of wood affects how much energy it produces. Hardwoods like oak or ash are denser and heavier than softwoods like pine, providing more heat per cubic metre.

2. What Is a Builder’s Bag?

A builder’s bag (also known as a bulk bag, dumpy bag, or ton bag) is a tough woven sack originally used in the construction industry to carry heavy materials like sand or gravel.

In the context of firewood, these bags are often reused to deliver logs. Although called a “ton” bag, this name can be misleading when applied to firewood.

A typical builder’s bag used for logs has dimensions around 0.8m × 0.8m × 0.8m, which gives a maximum loose volume of approximately 0.5 to 0.7 cubic metres depending on the fill. The actual volume of wood (when stacked) inside a builder’s bag is significantly less than a true cubic metre.

3. Builders Bag vs Cubic Metre Logs: Side-by-Side Comparison

Measurement	Builder’s Bag	Cubic Metre of Firewood
Approximate Volume	0.5 – 0.7 m³ (loose)	1.0 m³ (loose)
Stacked Volume	~0.3 – 0.5 m³	~0.6 – 0.7 m³
Typical Weight	200 – 300 kg (hardwood)	500 – 700 kg (hardwood)
Average Number of Logs	200 – 400	400 – 600

The takeaway? A builder’s bag usually holds about half to two-thirds the amount of firewood found in a loose cubic metre.

4. Why This Matters (Especially in the UK)

Understanding firewood size comparison UK standards is essential. Some suppliers list volume by the bag size, while others sell by cubic metres. Without clear stacking and moisture information, customers might believe they’re getting more wood than they actually are.

Moisture content also plays a major role. Firewood that’s not properly dried can contain a large amount of water, reducing its burn efficiency and heat output. Properly seasoned or kiln-dried wood with a moisture content of under 20% will burn cleaner and hotter.

5. What You’re Actually Paying For

Many people wrongly assume a builder’s bag contains a ton of firewood. In reality, it rarely weighs more than 300 kg when filled with seasoned hardwood logs. A true cubic metre of kiln-dried hardwood can weigh up to 700 kg.

So if you’re paying less for a builder’s bag, you’re also likely getting significantly less firewood—not just a cheaper deal.

6. How to Make a Smart Choice

Here are some helpful tips for comparing firewood quantities and getting the best value:

Ask about actual volume: Is it measured loose or stacked?
Check bag dimensions: Sizes can vary widely between suppliers.
Insist on low moisture content: Ideally 20% or less.
Look at the price per kilowatt hour (kWh): Some hardwoods give better heat per log.
Match the order to your storage space: If you can store more, a full cubic metre often offers better value.

Final Thoughts

To summarise:

A cubic metre of firewood is significantly more than a builder’s bag—typically by 30% to 50% in volume.
A builder’s bag is a convenient option, especially where space or access is limited, but it provides less heat output overall.
Comparing firewood by weight, moisture content, and burn quality is more reliable than simply looking at price or volume alone.

By knowing the key differences and asking the right questions, you can avoid buying blind and instead ensure you’re getting quality firewood at a fair price.

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