8 free calculators for Australian tradies, builders, and renovators.
These eight calculators cover the everyday estimating jobs on an Australian building or renovation project — working out how much material to order, and setting out to the right dimensions. All work in metric.
| Your job | Use this |
|---|---|
| Pouring a slab, footing or path | Concrete Calculator |
| Setting fence posts in concrete | Concrete Calculator (post-hole mode) |
| Gravel driveway or decorative stone | Gravel Calculator |
| Mulching garden beds | Mulch Calculator |
| Tiling a floor, wall or bathroom | Tile Calculator |
| Estimating a roof | Roofing Calculator |
| Setting out a staircase | Stair Calculator |
| Measuring floor area | Square Metre Calculator |
| Sizing an air conditioner | BTU Calculator |
Concrete, gravel, road base, sand and mulch are all spread over an area to a depth, so the volume in cubic metres is area multiplied by depth — with every measurement converted to metres first. A 100mm depth is 0.1 metres, not 100. Leaving depth in millimetres is the single most common estimating error, and it makes the answer a thousand times too big.
Your calculated figure is what ends up in place if nothing is spilled, no ground is uneven, and nothing is cut to fit. That never happens. A wastage allowance — commonly around 5–10%, and more for large tiles or complex layouts — protects you from running out partway through, which is almost always worse and more expensive than a small over-order.
Bulk materials are calculated by volume but often sold by weight, which is where estimates go wrong. Gravel and road base sit around 1.5 tonnes per cubic metre, so a volume in cubic metres has to be converted before ordering by the tonne — one cubic metre is not one tonne. Concrete is bought either as 20kg bags for small jobs or ready-mix by the cubic metre for anything shed-sized and up.
Calculators: Concrete · Gravel · Mulch
Guides: Concrete: slabs, post holes & cost · Gravel & mulch: ordering and cost
Both are estimated from an area, then adjusted. Tiling adds wastage for cuts — more for large-format tiles and patterns — and is ordered by the box, so you round up. Roofing has an extra twist: the true sloped area is larger than the building footprint because the roof is pitched, so ordering to the plan area always leaves you short.
Calculators: Tile · Roofing
Guides: Tiling & roofing: quantities, wastage & cost
Stairs are governed by the National Construction Code: risers and goings must fall within set limits and be consistent across a flight, because uneven steps are a genuine hazard. Floor area in square metres feeds flooring, paint and air conditioning estimates. Air conditioning is sized in kilowatts and BTU per hour — around 0.15 kW per square metre is a starting point, adjusted for ceiling height, windows, insulation and climate.
Calculators: Stair · Square Metre · BTU / Air Conditioning
Guides: Stairs, square metres & air conditioning
How do I calculate how much concrete or gravel I need?
Multiply length by width by depth, with every measurement in metres, to get the volume in cubic metres. Convert millimetre depths first — 100mm is 0.1m. Then add 5 to 10 per cent for wastage before ordering.
Why isn't one cubic metre the same as one tonne?
Because it depends on the material's density. Gravel and road base are around 1.5 tonnes per cubic metre, so 3 cubic metres is about 4.5 tonnes. Many suppliers sell by weight, so ask for the density and convert before ordering.
How much wastage should I allow?
Around 5 to 10 per cent for most materials and layouts. Allow more for large-format tiles, diagonal or herringbone patterns, small rooms with many cuts, and structural fill that compacts. Running out partway through a job is worse than a small over-order.
Why is a roof bigger than the house footprint?
Because the roof slopes, so its true surface area is larger than the flat plan area measured from above. A pitched roof over a 12m by 8m footprint can be around 104 square metres at a 22.5 degree pitch. Always order roofing to the sloped area.
What size air conditioner do I need?
As a rough guide, allow about 0.15 kW of cooling per square metre for a standard insulated room, so a 20 square metre room needs roughly 3 kW or about 10,200 BTU per hour. Ceiling height, windows, orientation, insulation and climate all adjust this, and an installer can do a proper heat-load calculation.
Do these calculators replace a builder or the building code?
No. They are estimating tools for planning and budgeting. Structural work, stairs, and many renovations must comply with the National Construction Code and relevant Australian Standards, and may need council approval and licensed trades. Always confirm on site and with a professional before ordering or building.
None of these calculators shows a price, because material costs change constantly and vary by region, supplier and specification. The reliable approach is the same for every job: use the calculator to fix your quantity, add a wastage allowance, then get two or three local quotes against that exact figure. Remember the raw material is often not the biggest cost — formwork, reinforcement, adhesive, waterproofing, flashings, base preparation and labour frequently add up to more.
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Important: MegaCalcOnline provides general information and educational calculators only. Nothing here is engineering, building, or trade advice. Quantities are estimates — always confirm measurements on site, follow manufacturer coverage figures, and consult a licensed builder or your supplier before ordering. Building and renovation work may require council approval and must comply with the National Construction Code and relevant Australian Standards.
Whether you're pouring a concrete slab, laying tiles, or estimating how much roofing material a job needs, getting quantities right the first time saves money and prevents the frustration of running short mid-project. The calculators on this page are built around the way Australian trades and DIY renovators actually measure and order materials.
Most experienced builders add a waste allowance — typically 5-10% — on top of the exact calculated quantity for materials like tiles, concrete, and roofing. This accounts for cuts, breakages, and pattern matching. Running short partway through a job often costs more in total than ordering slightly extra upfront, especially if a product batch or dye lot changes between orders.
A concrete slab's volume depends on length, width, and thickness — and thickness requirements change based on what the slab needs to support. A garden path needs far less depth than a driveway rated for vehicle loads. Always check the appropriate thickness for your specific application before ordering, since concrete is priced and delivered by volume (cubic metres), not area.
Roofing material calculations need to account for roof pitch, not just the building's footprint — a steeply pitched roof has significantly more surface area than the same building with a low-pitch roof. Tiling calculations similarly need to account for tile size, grout lines, and pattern (straight lay versus diagonal, which typically wastes more material).
How much extra material should I order to cover waste?
A common rule of thumb is 5-10% extra for straightforward jobs, and up to 15% for complex cuts, diagonal tile patterns, or irregularly shaped areas. Always round up to the nearest full unit your supplier sells in.
Do these calculators replace the need for a structural engineer?
No. These tools estimate material quantities for planning and budgeting purposes only. Any structural work, load-bearing calculations, or council-regulated construction should be assessed by a qualified engineer or licensed builder.
Why does roof pitch matter for roofing material calculations?
A pitched roof has more actual surface area than its flat footprint suggests, because the sloped surface is longer than the horizontal distance it covers. Steeper pitches require proportionally more roofing material for the same building footprint.
General estimating guidance only. Always confirm quantities with your supplier and check local building codes before starting structural work.
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