Building Cost Calculator

A worked example

With the calculator’s starting values (floor area: 150 m²; building type: House (standard); province: Gauteng), it returns:

• Typical estimate: R 1 650 000 (R 11 000/m² × 150 m²)
• Budget range: R 1 350 000 – R 2 100 000 (low to high quality)
• Rate per m²: R 9 000 – R 14 000 (gauteng factor applied)

How the estimate is built

The calculator multiplies your floor area by a rate per square metre for the building type, then adjusts that rate for the province. The base rates are Gauteng-anchored figures from the AECOM Africa Property & Construction Cost Guide 2025/26, and the provincial factors come from ooba's 2025/26 build-cost table. It is the same model behind the city cost pages, so the two always agree.

You get three numbers. The low rate suits a plain specification on an easy site. The typical rate is where most projects of that type land. The high rate covers heavier finishes, more complex structure and difficult sites. Treat the range as the honest answer at this stage and the typical figure as a midpoint, not a promise.

Measuring the floor area

Use the gross floor area: every enclosed floor, measured to the outside face of the external walls. For a double-storey house, add both floors. Leave out open patios, carports and garden walls, and price garages and covered verandas separately at a lower rate, because they carry far fewer finishes and services than habitable rooms.

If you only have a rough idea of size, work from the rooms you need. A three-bedroom, two-bathroom house with an open-plan living area usually lands somewhere between 140 and 200 m² before the garage, depending on how generous the rooms are.

What moves a project off the benchmark

A per-m² rate assumes an average project. Yours will differ in some of these ways:

• Ground conditions. Clay, dolomite, fill or a high water table can multiply foundation cost.
• Slope. A steep stand needs retaining, stepped foundations and more earthworks.
• Shape. An articulated plan has more external wall per square metre of floor than a simple rectangle.
• Specification. Finishes, joinery and glazing move the rate more than any structural choice on a house.
• Access. A tight urban site or a remote rural one both add cost through handling and transport.

Turning the estimate into a budget

Add the costs the rate leaves out: professional fees, municipal plan and connection charges, NHBRC enrolment for a new home, boundary walls and paving, and VAT at 15%. Then add a contingency for the unknowns, which should be larger at concept stage than once drawings exist. When there is a sketch plan, split the budget by element with the elemental estimate tool, and when there is a bill of quantities, price it with the BoQ pricer.