What Size Logs for a Wood Burner? Log Length Calculator

Measure the inside of your stove's firebox, put the width and depth in below, and this tells you the longest log that will sit in it, the standard cut length to ask your log merchant for, and whether the logs you already have will fit. The point most people miss: the length that matters is the inside of the firebox, not the outside of the stove, and a log needs a gap at each end. A log that is wedged in or presses on the glass blackens it, can crack it when it expands, and is a fight to load safely.

How to measure your firebox

Open the door once the stove is completely cold and measure inside, from firebrick to firebrick. Take the width across the front just behind the glass, and the depth from the inside of the glass to the back bricks. If the stove has a log guard or fret along the front, measure depth from the back of the guard, because that is where the logs actually sit. Use the narrowest point: some fireboxes taper towards the back.

Side to side or front to back?

Most stoves are loaded with logs lying side to side, parallel with the glass, which is why the width usually sets the longest log. Some manuals recommend loading front to back instead, and some state a maximum log length outright. If your manual gives a loading direction or a figure, follow it: it overrides anything this calculator says.

Standard log lengths in the UK

Log merchants mostly cut to a few standard lengths, often quoted in inches. The calculator matches your firebox to the longest of these that fits with the gap you chose:

• 20cm (8in): for small and compact stoves
• 25cm (10in): the most common "stove length" log
• 30cm (12in): medium stoves with wider fireboxes
• 40cm (16in) and 50cm (20in): large stoves, inset fires and open fires

If your firebox sits between two lengths, buy the shorter one. A slightly short log burns perfectly well; a slightly long one is the one that ends up jammed against the glass.

How thick should the logs be?

Length is only half of it. Split logs burn best when they are roughly the thickness of your wrist to the thickness of your forearm. Very thick rounds smoulder because the air cannot get at enough surface, and they take far longer to season. If you buy unsplit rounds, split anything you cannot comfortably hold in one hand. Small stoves need thinner logs again, and kindling should be thinner than your thumb.

Whatever size you burn, it needs to be dry. Wood sold in single units of less than 2m³ in England has to be certified Ready to Burn, which means a moisture content of 20% or less. You can check your own with the firewood moisture content calculator, and work out how much to buy for the season with the firewood calculator.