Australian trade and construction calculators

Questions these calculators answer

How much concrete do I need?

Multiply length by width by depth in metres to get cubic metres. A slab 4 m × 3 m × 100 mm is 4 × 3 × 0.1 = 1.2 m³. A 20 kg bag of pre-mixed concrete yields roughly 0.0107 m³, so that slab needs about 112 bags — which is well past the point where ready-mix is cheaper and far quicker.

How much mulch do I need?

Multiply the bed area in square metres by the depth in metres. A 20 m² bed at 75 mm deep needs 20 × 0.075 = 1.5 cubic metres. In 50 litre bags that is 30 bags; in bulk it is about a level box-trailer load. Anything under 50 mm deep will not suppress weeds for long.

How many pavers do I need?

Divide the area to be paved by the area of one paver, then add a wastage allowance for cuts. A 30 m² patio with 400 × 400 mm pavers needs 30 ÷ 0.16 = 188 pavers, plus about 10% for cuts — call it 207. Add more if the area has curves or angled edges.

How do you calculate tank capacity in litres?

Work out the volume in cubic metres, then multiply by 1,000. An upright cylindrical tank is πr²h; a rectangular tank is length × width × height. A tank 1.8 m across and 2.1 m tall holds 5.34 m³, which is 5,340 litres. A horizontal tank filled part way needs the circular-segment formula instead.

How do you calculate gas strut force?

Balance the moments about the hinge. The lid's weight acting at its centre of gravity creates a turning moment; the strut has to produce an equal one from its own mounting distance. Force = (weight × 9.81 × distance to centre of gravity) ÷ (distance to strut mount), divided by the number of struts.

How do you calculate stair riser height?

Divide the total rise by a whole number of risers until the result lands in the allowable range. A 2,700 mm floor-to-floor rise divided by 15 gives 180 mm risers — inside the range for a private stair. Then check the riser and going together against the code relationship, because each is constrained by the other.

How long does a wheelchair ramp need to be?

At the 1:14 maximum AS 1428.1 allows for an accessible ramp, every 1 metre of rise needs 14 metres of ramp. A 600 millimetre step therefore needs 8.4 metres of ramp — plus landings, which add their own length. At the gentler 1:20 walkway gradient the same rise needs 12 metres.

How much paint do I need for a room?

Work out the wall area (room perimeter × height), subtract doors and windows, add the ceiling if you are painting it, then divide by the tin's coverage and multiply by the coats. A 4.5 × 3.8 m room with a 2.4 m ceiling, two doors and one window needs about 6.4 litres for two coats at 12 m² a litre, including a 10% allowance.

How many bricks do I need per square metre?

A standard 230 × 110 × 76 mm brick laid with 10 mm joints covers 240 × 86 mm of wall face, which is about 48 bricks per square metre for a single skin. A 12 m long, 2.4 m high wall with 3.6 m² of openings is 25.2 m² and needs about 1282 bricks with a 5% allowance.

How many tiles do I need?

Divide the area by the area one tile covers including its grout line, then add an allowance for cuts: 10% for a straight layout, more for diagonal or patterned layouts. A 12 m² floor with 600 × 600 mm tiles and 3 mm grout needs about 33 tiles, or 37 with a 10% allowance.

How many sleepers do I need for a retaining wall?

Divide the wall height by the sleeper height to get the courses, and the wall length by the sleeper length to get the sleepers in each course. A 9.6 m long, 0.8 m high wall of 2.4 m × 200 mm sleepers is 4 courses of 4 sleepers, or 16 in all, with 5 posts.

How many Colorbond panels do I need?

Subtract the gate openings from the fence length, divide by the panel width and round up. At 2.35 m a panel, 24 m of fence with one 1 m gate is 10 panels, with 15 posts including both gate posts and two corners, and two rails per bay.

How do I calculate roof pitch?

Roof pitch in degrees is the angle whose tangent is the rise divided by the run. A 1 in 4 pitch (rise 1 for every 4 of run) is 14.04 degrees, or a 25% grade. To get the roof area, divide the plan area by the cosine of the pitch angle: at 22.5 degrees the roof is about 8% bigger than the area it covers on the ground.

How many sheets of plasterboard do I need?

Divide the area to be lined by the area of one sheet and add 10% for cutting waste. A 1.2 × 2.4 m sheet covers 2.88 m². A room with 14 m of wall at 2.4 m and 3.5 m² of openings is 30.1 m² and needs about 12 sheets of 2.4 m.

How many insulation batts do I need?

Divide the area to be insulated by what one pack covers, after taking off the part of the area taken up by framing, and add a little for waste. A 150 m² ceiling with 7.8 m² per pack needs about 20 packs, with a 5% allowance and 5% of the area taken by joists.

How much gravel do I need?

Multiply length by width by depth in metres to get cubic metres, add an allowance, and multiply by the density to get tonnes. A 8 × 3 m area at 100 mm deep is 2.40 m³, which is about 4.2 tonnes of gravel at 1.6 t/m³ with a 10% allowance.

How much soil do I need?

Multiply length by width by depth in metres to get cubic metres, add an allowance, and multiply by the density to get tonnes. A 6 × 4 m area at 150 mm deep is 3.60 m³, which is about 5.4 tonnes of soil at 1.3 t/m³ with a 15% allowance.

How much sand do I need?

Multiply length by width by depth in metres to get cubic metres, add an allowance, and multiply by the density to get tonnes. A 4 × 3 m area at 30 mm deep is 0.36 m³, which is about 0.6 tonnes of sand at 1.6 t/m³ with a 10% allowance.

How many decking boards do I need?

Divide the deck's width by the board width plus the gap to get the number of boards across, and multiply by the board length needed to span the deck. A 5.0 × 3.6 m deck using 140 mm boards with a 5 mm gap needs 25 rows of boards, and 13 joists at 450 mm centres.

How do I calculate timber volume and lineal metres?

Lineal metres are the number of pieces times their length. Volume is that length times the section's width and thickness in metres. 20 pieces of 90 × 45 mm at 3.0 m is 60 lineal metres and 0.243 cubic metres, and weighs about 158 kg at 650 kg per cubic metre.

How much flooring do I need?

Multiply length by width, add 10% for cuts and divide by the area of a pack, rounding up. A 5 m by 4 m room is 20 m², 22.0 m² with waste, which is 10 packs of 2.2 m² each. Diagonal layouts and patterns need 15% or more.

How many rolls of turf do I need?

Divide the lawn area by the area of a roll and add a margin for cuts. A 60 m² lawn with rolls of 1 m² and 5% extra needs 63 rolls. A 75 mm layer of soil under it is 4.5 m³.

How many rolls of wallpaper do I need?

Work out how many strips the walls need, how many strips one roll yields, then divide. A room with 14 m of wall and 2.4 m high needs 27 strips of 53 cm paper. A 10 m roll gives 4 strips, so you need 7 rolls. A pattern repeat reduces the strips per roll and raises the total.