Timber & Framing
Wood Shrinkage Calculator
Estimates dimensional change in timber from moisture content change
Updated 13 May 2026 · Live
What this tool does
Estimates dimensional change in timber from moisture content change.
Wood Shrinkage Calculator — estimate based on the {initial_width_mm} mm initial width and moisture change you enter, giving a predicted shrinkage of {result}.
People also use
Formula Used
How the wood shrinkage calculator works
Estimates dimensional change in timber from moisture content change. The calculator takes your dimensions and supplier rates, applies a standard UK trade formula, and returns a quantity with an indicative cost. Every figure is an estimate — site conditions always move the final number.
Typical UK timber and framing wastage
Timber wastage runs 5–10% on straight cuts, 10–15% for angled or notched framing. Lengths chosen to minimise splicing tend to cost less — a 4.8 m joist often works out cheaper than two 2.4 m pieces. Our defaults reflect common UK trade allowances, and can be adjusted upwards for non-standard geometry or downwards where experience supports a lower figure.
What this tool does not do
It does not replace a professional quote, factor regional pricing, assess structural adequacy, or confirm Building Regulations compliance. Those remain the responsibility of a suitably qualified designer, surveyor, or your building control officer.
On-site considerations for wood shrinkage
Check grading stamps (C16, C24) on every length — structural timber must be graded to BS EN 14081. Moisture content should be below 20% for internal use; above this, shrinkage and movement are significant.
Building Regulations and compliance
Structural framing is subject to Approved Document A. Span tables in TRADA guidance are indicative only — your building control officer will want calculations for anything unusual. When in doubt, a pre-application enquiry to the local authority can give early clarity, which tends to be less costly than retrospective correction.
Before you order
Buy treated timber (UC3 for exposed, UC4 for ground contact) even for internal joists near wet areas. The premium is small next to the labour cost of a rebuild. Cross-checking the calculator’s output against a supplier quote helps catch differences in pricing assumptions — ask for exact product specifications (grade, finish, batch number) and confirm delivery timescales against your programme.
Adjusting the defaults
Every input in this calculator is editable. Enter your own dimensions, supplier prices, and wastage allowance — the output recalculates instantly. If the defaults feel off for your region or project type, your own numbers always override them.
Using this wood shrinkage calculator alongside other BuildMetricLab tools
This calculator works best as part of a planning workflow. Pair the quantity with our project contingency, labour-hours, and material-cost calculators to build a complete estimate before you pick up the phone to a supplier. All BuildMetricLab tools run entirely in your browser — no sign-up, no data sent anywhere, and every formula is shown on-page so you can audit the maths.
Sources & methodology
Estimates dimensional change in timber from moisture content change. Every result is calculated from the values you enter, and all inputs are editable.
Frequently asked questions
Are wood shrinkage calculator results accurate enough to order materials?
Use them as a starting estimate only. Verifying the final quantity with your supplier or contractor before ordering is good practice — site conditions, wastage and cut-offs all affect the true figure.
What shrinkage coefficient should I use?
Typical values are around 0.0025 per %MC for tangential (plain-sawn) shrinkage in softwood, and around 0.0015 per %MC for radial (quarter-sawn) shrinkage. Species and grain orientation both affect the true figure, so use a value from the timber supplier's data sheet where precision matters.
Is professional advice still needed for this?
No. This tool is a planning estimator. For works that affect structure, Building Regulations, Party Wall, gas, electrics, drainage to a sewer, or similar, consult a suitably qualified professional.
Can I change the unit prices?
Yes — every price field is editable. Plug in your supplier's quote to get a total that matches your project.
Spotted something off?
Calculations or display — let us know.
Related tools
Calculators from other categories that planners often reach for next.