Work it out.
Calculators tailored to the carpentry trade: measure the material consumption, divide the run into centre-to-centre spacing, find the rafter length, set out the staircase and work out the concrete. Enter your own values — the result updates live.
Step V — Directory
The guided workflow: answer house dimensions and chosen roofing material and get the complete roof specification brought together in one flow.
Step A — Measurement & material consumption
Start here: convert area into a number of boards/sheets and linear metres — with your own waste allowance.
Step B — Spacing & centre distance
Count rafters, battens and posts correctly over a span based on the centre spacing (cc).
Step C — Roof & rafters
Find the rafter length and roof pitch of a symmetrical gable roof using Pythagoras.
Rafter length & roof pitch
Pythagoras on a symmetrical gable roof
Batten spacing to roof tile
Center-to-center distance based on stone dimensions
Roof area, battens and tiles
The roof area along the roof, batten rows and number of roof tiles
Batten division
Same batten spacing between bottom batten and top batten
Rafter section
Plumb line, vertical and bird's mouth from roof pitch
Step D — Stairs
Set the riser, going, and number of steps according to Blondel's stride formula.
Step E — Concrete & foundation
Calculate the concrete volume for a rectangular pour, so the concrete can be ordered in one go.
Step F — Building physics & material
Wood moisture and shrinkage, U-value against BR18, and how much cross-section burns away — the trade's physics check.
Shrinkage & moisture movement
Dimensional change with changing wood moisture
U-value — timber-frame wall/roof/floor
Heat loss through a flat construction
BR18 climate requirement — LCA against the limit value
Climate impact per m² per year compared with § 298
Fire charring & residual cross-section
How much wood burns away over time
Vapour barrier Sd-value
Diffusion resistance for a layered vapor barrier
Insulation thickness for a U-value
The reciprocal U-value: how thick should the insulation be?
Step G — Plot & siting
The house, carport or shed on the plot: distance and height to the boundary under the building right.
Tools that work in all subjects
Maths and templates that work in every trade — and at school. Every tool shows the formula and the working with your own numbers.
- Pythagorasa² + b² = c²Find the missing side, set out a right angle, check whether a room is square, and find the space diagonal.
- Area and perimeterm²Rectangle, triangle, trapezium, circle and composite shapes — area and perimeter.
- Volume and surface aream³ · lBox, cylinder, cone, sphere, pyramid, prism, pipe and frustum — also in litres.
- Percent%Percentage of, how many per cent, percentage change, discount and VAT.
- Scale and ratios1 : 50From drawing to reality, area and volume to scale, the rule of three and dividing in a ratio.
- Unit convertermm ↔ mFrom mm to km, Pa to bar and kB to GB — with the unit staircase.
- Time calculations and the clockt : minTime between two clock times, add time, and 1.75 h = 1 h 45 min for the timesheet.
- Slope and fall% · ° · 1:xFall from level to level, in per cent, per mille, degrees and mm per metre — and the height difference.
- Material consumption including wastem² + %Boards, paint, battens at c/c spacing and packs — for a composite surface or a whole room, with waste.