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How to Calculate Timber Volume
Calculating timber volume is essential for ordering the correct amount of material for your construction or woodworking project. The volume determines how much timber you need and helps estimate costs.
Basic Volume Formula
For rectangular timber pieces, the volume calculation is straightforward. Multiply the length, width, and thickness together. When working in metric units, the formula is:
Volume (m³) = Length (m) × Width (m) × Thickness (m)
If your measurements are in millimetres, convert them to metres by dividing by 1,000 before multiplying. For example, a piece measuring 2.4 metres long, 100mm wide, and 50mm thick would be: 2.4 × 0.1 × 0.05 = 0.012 cubic metres.
Board Feet Calculation
Board feet is a common measurement in timber, particularly for hardwoods. One board foot equals a piece of timber 12 inches long, 12 inches wide, and 1 inch thick. The formula is:
Board Feet = (Length in feet × Width in inches × Thickness in inches) ÷ 12
This measurement helps when comparing prices across different suppliers and timber sizes.
Converting Between Units
When working with timber, you may need to convert between metric and imperial units. One cubic metre equals 35.3147 cubic feet, and one cubic foot contains 12 board feet. These conversions are important when sourcing timber from different regions or comparing specifications.
Standard UK Timber Sizes
Timber in the UK is available in standard sizes regulated by British and European standards. Knowing these sizes helps with planning and ordering.
Common Structural Softwood Sizes
Structural softwood typically comes in these nominal cross-sections:
| Width × Thickness | Common Applications |
|---|---|
| 47mm × 50mm | Wall studs, light framing |
| 47mm × 75mm | Joists, rafters, general framing |
| 47mm × 100mm | Floor joists, roof rafters |
| 47mm × 150mm | Floor joists, beams |
| 47mm × 200mm | Large joists, structural beams |
CLS Timber Dimensions
Canadian Lumber Standard (CLS) timber is popular for timber frame construction. Common sizes include 38mm × 63mm, 38mm × 89mm, and 38mm × 140mm. CLS timber features rounded edges and comes kiln-dried, making it stable and ready for immediate use.
Standard Lengths
Timber is typically available in lengths from 2.4 metres to 4.8 metres, increasing in 0.3-metre increments. The most common lengths are 2.4m, 3.0m, 3.6m, and 4.8m. Longer lengths may be available on special order but can be more expensive and difficult to transport.
Timber Pricing in the UK
Timber prices vary based on species, grade, treatment, and market conditions. Softwood prices are generally lower than hardwood, and treated timber costs more than untreated.
Current Price Ranges
As of 2025, softwood structural timber typically costs between £400 and £600 per cubic metre. Standard hardwoods like oak or ash range from £600 to £1,000 per cubic metre, whilst premium hardwoods can exceed £1,200 per cubic metre. These prices fluctuate based on supply, demand, and economic conditions.
Factors Affecting Timber Costs
Several factors influence timber pricing. Strength grading (C16, C24) affects structural timber costs, with higher grades commanding premium prices. Treatment for exterior use, such as pressure treatment, adds 15-25% to the base cost. Moisture content also matters – kiln-dried timber costs more than green timber but offers better stability and immediate usability.
Buying Tips
When purchasing timber, buy in bulk to secure better rates. Many suppliers offer discounts for larger orders. Check multiple suppliers, as prices can vary significantly between merchants and regions. Consider delivery costs, which can be substantial for heavy timber orders. Finally, order 10-15% extra to account for waste, cutting errors, and defects.
Frequently Asked Questions
What is the difference between cubic metres and board feet?
Cubic metres measure volume in the metric system and are standard in the UK. Board feet is an imperial measurement commonly used for hardwood lumber, where one board foot equals 144 cubic inches. One cubic metre equals approximately 423.776 board feet.
How do I calculate timber needed for decking?
Measure the total area of your deck in square metres, then divide by the coverage area of one board. Add 10-15% for cuts, waste, and future repairs. Multiply by the board thickness to get total volume, which helps determine cost and delivery requirements.
What does nominal size mean?
Nominal size refers to the size before planing or finishing. Actual finished dimensions are slightly smaller. For example, timber sold as 47mm × 100mm is the target size after sawing, but planed timber may measure 45mm × 95mm due to surface finishing.
Should I buy treated or untreated timber?
Use treated timber for any exterior application or where moisture exposure is likely. Pressure-treated timber resists rot and insect damage. Untreated timber suits interior applications and is less expensive. Never use untreated timber outdoors or in damp conditions.
What is the weight of timber per cubic metre?
Weight varies by species and moisture content. Softwoods like pine typically weigh 450-550 kg per cubic metre when dry. Hardwoods are denser – oak weighs around 720 kg/m³, whilst ash is approximately 690 kg/m³. Green (unseasoned) timber weighs significantly more due to moisture content.
How accurate should my timber calculations be?
Always add a waste factor to your calculations. For straightforward projects, add 10%. For complex projects with many cuts or inexperienced workers, add 15-20%. Timber merchants sell in full pieces, so round up your quantities accordingly.
Can I mix different timber grades in a project?
For structural applications, never mix grades without consulting a structural engineer. Each grade has specific load-bearing capacities. For non-structural work like cladding or fencing, mixing grades is acceptable, though appearance may vary between pieces.
What does C16 and C24 mean?
These are strength classifications for structural timber under European standards. C24 is stronger and stiffer than C16, allowing for larger spans and heavier loads. C24 costs approximately 10-15% more than C16. Building regulations specify which grade is required for different applications.