Timber Calculator
Work out how much timber you need for any job. Enter the piece length, cross-section dimensions, quantity, and grade to get total linear metres, volume, weight, and an estimated materials cost.
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How to use this timber calculator
Start by entering the length of each individual piece in metres — for example, 2.4m for a standard stud or 4.8m for a floor joist. Then select the cross-section size: width and depth in millimetres. The most common structural sizes in the UK are 47×100mm (stud walling), 47×150mm (floor joists), 47×200mm (longer span joists), and 47×225mm (rafters and headers).
Enter the quantity — the number of pieces you need at that length. Add a wastage percentage to account for cuts, defects, and any pieces that get damaged on site. Ten per cent is standard for most framing jobs; for complex cuts or smaller sections you might allow 15%.
Select your timber grade. C16 covers most standard domestic work. C24 is specified where structural performance is critical — long span joists, rafter sections, or anywhere a structural engineer has given you a specification. Green oak is used for traditional frame buildings, barn conversions, and exposed structural features. Treated softwood adds preservative treatment and is the right choice for ground-level framing, decking subframes, and anywhere moisture is a concern.
The results show total linear metres, volume in m³, approximate weight, and a guide materials cost based on current UK timber prices. Use the cost figure as a starting point for your quote — always get a firm price from your merchant before committing to a contract.
Frequently asked questions
What is the difference between C16 and C24 timber?
C16 is standard structural grade softwood suitable for most floor joists, stud walls, and general framing. C24 has a higher strength rating and is specified where loads are heavier — roofing rafters, longer span joists, and engineered frames often call for C24. The visual difference is minimal but C24 is stiffer and less prone to deflection over long spans.
How much does structural timber cost in the UK?
As a rough guide for 2025/26, C16 softwood costs around £250–£300 per m³, C24 is typically £300–£350/m³, and treated softwood runs £320–£380/m³. Green oak is significantly more expensive at £700–£1,000/m³ depending on the section size and supplier. Prices fluctuate with global supply chains — always get a current quote from your merchant.
How do I calculate how much timber I need?
Multiply the length of each piece by the number of pieces to get total linear metres. Then multiply by the cross-section area (width × depth in metres) to get volume in m³. Add 10–15% for wastage from cuts and defects. Our calculator handles all of this automatically once you enter your dimensions, quantity, and wastage percentage.
What size timber do I need for floor joists?
The required joist size depends on span, load, and species. A common rule of thumb for C16 softwood at 400mm centres with domestic loading: spans up to 2.4m use 47×97mm, up to 3.0m use 47×120mm, up to 3.6m use 47×145mm, and up to 4.2m use 47×170mm. Always check span tables in Approved Document A or your structural engineer's specification.
Should I use C16 or C24 for roof rafters?
For most domestic pitched roofs with standard loading, C16 is acceptable for shorter spans. C24 is the safer choice for spans over 2.5m, roofs with heavier tiles, or where the specification requires it. Many builders default to C24 throughout for peace of mind and to satisfy building control without needing additional calculations.
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