Fire Pit Clearance & Firewood Calculator
Positioning a fire pit too close to fences, decking or overhanging branches is a real fire risk, and running out of wood halfway through the evening cuts things short. Choose your fire pit size and planned burn time below for a safe clearance distance and a firewood estimate.
Check fire pit clearance and firewood needed
Choose your fire pit size and how many hours you plan to burn it for.
Keep at least 3.5m clear from fences, sheds, decking and overhanging branches in every direction.
9.0kg of firewood
That's around 1 × 10kg nets for 3 hours of burning.
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Frequently asked questions
How far should a fire pit be from a fence or shed?
A minimum of around 3m from any structure, fence, hedge or overhanging branches is a common safety guideline, with larger fire pits needing more clearance due to bigger flames and more radiant heat. Always check your fire pit manufacturer's specific guidance too.
Can I use a fire pit on decking?
Standard wood-burning fire pits are generally not recommended directly on timber decking due to fire risk and scorching, even with a raised base — look for a heatproof fire pit mat, paving slabs, or gravel area instead.
What firewood burns best in a fire pit?
Well-seasoned hardwood (like oak, ash or birch) with a moisture content under 20% burns hotter, cleaner and longer than unseasoned or softwood, which tends to smoke more and burn out faster.
Do I need council permission for a garden fire pit?
In most cases, a domestic fire pit used responsibly doesn't need permission, but you should still be mindful of smoke drifting into neighbours' gardens, avoid burning on very windy days, and check for any local smoke control area restrictions.
How this Calculator Works
This calculator uses a standardised clearance distance of 6 metres from any combustible material – this is the minimum recommended by many UK fire safety guidelines. The tool first asks you to input the diameter of your fire pit in centimetres. Then, it multiplies this diameter by a factor of approximately 1.37m (1.37 metres) to determine the required clearance distance in metres, accounting for wind exposure and potential heat spread. The firewood calculation is based on an average burn time of 2 hours per log, assuming a typical wood length of 30cm and a fuel density of 8.4 MJ/kg – this results in an approximate amount of wood needed.
Firewood Types & Burn Times (UK)
- **Softwoods (e.g., Pine, Fir):** Have a lower BTU content (around 13-16 MJ/kg) and burn faster – expect around 90 minutes of continuous burning per log. Commonly available in UK garden centres at approximately £8 - £12 per full cord.
- **Hardwoods (e.g., Oak, Ash):** Offer a higher BTU content (around 17-20 MJ/kg) and burn slower, providing longer heat output – typically 120 minutes of continuous burning per log. Premium oak can cost around £25 - £40 per full cord.
- **Seasoned Wood is Key:** Regardless of the type, ensuring your wood is properly seasoned (dried for at least 6-12 months) significantly improves burn efficiency and reduces smoke output. Wet wood burns inefficiently and produces harmful creosote.
- **Log Length Matters:** Shorter logs burn faster than longer ones; a standard log length of 30cm to 45cm is common in the UK.
- **Wood Moisture Content:** Aim for a moisture content below 20% – this can be measured with a moisture meter, costing around £30-£60 online.
Worked Example: A 90cm Fire Pit & Evening Burn
Let’s say you've purchased a circular fire pit with a diameter of 90cm (0.9m). Using the calculator, we multiply 0.9m by 1.37m, resulting in a clearance distance of approximately 1.23m from any structures. This means you should position your fire pit at least 1.23 metres away from fences, sheds, or trees. Furthermore, if you plan to burn for two hours using seasoned softwood logs (8.4 MJ/kg) and assume each log is 30cm long, the calculator would estimate needing around 9 logs. At a cost of £10 per log, this equates to a total firewood cost of £90 for that evening’s use – remember to factor in additional wood for longer burns or colder evenings.
More questions answered
What does the clearance distance actually mean?
The 6-metre clearance is a minimum recommended by UK fire safety guidelines. It’s designed to provide a buffer zone between your fire pit and any flammable materials, reducing the risk of accidental fires spreading. Local regulations may have stricter requirements, so always check with your local council.
What if my fire pit isn't perfectly circular?
The calculator assumes a circular shape for simplicity. If your fire pit is significantly different (e.g., square or rectangular), increase the clearance distance by approximately 10-20% to account for potential heat distortion and wind exposure.
How does wind affect the calculation?
Wind increases the risk of embers spreading, so you should always increase the clearance distance in windy conditions. A strong breeze could easily carry embers up to 15-20 metres – significantly more than the standard 6m.
Can I use this calculator for chimineas?
Yes, but be extra cautious! Chimineas are often constructed from timber and can generate high heat. Increase the clearance distance by at least 50% to provide a substantial safety margin – consider using a non-combustible base.
What if I only burn for an hour?
Reduce your firewood calculation proportionally. If you’re burning for one hour, halve the number of logs estimated in the worked example and adjust the quantity accordingly.
How accurate is the firewood burn time estimate?
The 2 hours per log burn time is an average; actual burn times will vary depending on wood type, moisture content, and airflow. Always monitor your fire carefully and adjust accordingly.
What should I do if embers escape from my fire pit?
Have a bucket of water or sand readily available to extinguish any escaping embers immediately. Never allow embers to spread beyond the designated clearance zone.
Where can I buy seasoned firewood in the UK?
Most reputable garden centres, timber merchants, and online retailers sell seasoned firewood in the UK. Look for wood that has been properly dried and stacked – a good indicator is its colour and weight.
Can I use treated wood for my fire pit?
No! Using treated wood (pressure-treated or chemically treated) is extremely dangerous as it releases toxic fumes when burned. Always use untreated natural wood for your fire pit.
What if the calculator gives me a clearance distance that's too large?
While safety is paramount, excessively large clearances can reduce the usability of your outdoor space. Double-check local regulations and consider alternative placement options while prioritizing safe distances – consulting with a fire marshal is recommended for critical installations.