Free building and home calculators
Quick, honest answers to the questions people ask before they build, renovate or buy. Free, no sign-up, and every result shows how it was worked out.
What size air conditioner do I need?
Enter the room and get the cooling and heating load in kW, plus the split-system size to look for. Takes about 30 seconds.
Open the calculator →How many solar panels do I need?
Enter your roof and your power use to get the number of panels, system size, yearly savings, payback time and a battery suggestion.
Open the calculator →Retaining wall calculator
Enter the wall height, what’s on top and your soil, and see the footing (base) size a cantilever wall needs to stop it sliding or tipping over.
Open the calculator →What size timber beam do I need?
Enter the span and what the beam holds up, and see the smallest timber size that works, with every common size checked.
Open the calculator →Is my driveway too steep?
Enter how far the garage is above or below the road and how far back it is. See the slope, whether cars will scrape, and the transitions you need.
Open the calculator →Got house plans?
Groundwork Houses mode reads the plans and checks wind, soil, bushfire, bracing, footings and setbacks in one go. You get an engineering brief to hand to your engineer, builder or certifier.
These calculators give first checks using simplified methods and typical values. Have a qualified engineer or licensed tradesperson confirm results before you build, buy or rely on them.