Construction cost estimator/calculator

Caveat lector! (Reader beware!)

Our construction cost calculator only gives an estimate of building costs. It is only suitable for use before any detailed plans are drawn. Note: You will need to adjust the default per-square-foot cost to a value more suitable for your area.

For accurate construction costs you will require detailed construction plans and the services of a professional estimator or licensed builder/contractor.

Also note: The cost of renovations are often impossible to estimate due to unseen structural issues in the building. However the cost of extensions can usually be determined as accurately as the cost of a new home.

If you speak to a few builders in your area you should be able to get reasonable per-square-foot costs for your own location and requirements. The assumptions on which the cost calculator is based are listed below. Please Note: The cost assumptions stated below do not apply to kit homes or project homes, which cost much less to build than custom homes.

Cost assumptions

Cost assumptions built into our construction cost calculator are as follows (but you can easily change them):

  • A custom designed house on an excellent site using basic finishes will cost $120/square foot.
  • A custom designed house on an excellent site using standard finishes will cost $165/square foot.
  • A custom designed house on an excellent site using luxury bathroom and kitchen fittings will cost at least $210/square foot.
  • If the site is “good”, but not excellent, add 7% to the cost (e.g. a slightly sloping block of land or land that requires some drainage).
  • If the site is “difficult”, add at least 20% to the cost (e.g. a steep block of land that or a block of land).
  • Renovations cost twice as much, per square foot, as new home construction or extensions.

Calculator Steps

 project type:
new home or extension         
On a per square foot (SF) basis
are invariably more expensive than building a new house or an extension to an existing home. Thus it is prudent to explore two cost saving options: (1) knock-down and rebuild, or (2) leave the current building essentially untouched and attach a new building using a walkway or some other mechanism.
size of house:


Select from small, medium or large to set defaults for the areas specified in the table of areas below.
Then change the default values to values appropriate for your renovation or new
house design. All areas must be specified in square-feet.
site conditions:


Flat/level blocks are of course the easiest & cheapest blocks to
build on and if this is the case with your property select “excellent”,
unless the block has water drainage or other complications, in which case select “difficult”.
Steeply sloped properties should also be marked as difficult.
Use “good” for slightly sloping properties.
quality of finishes:


Quality of finishes refers to PC items like toilets, tiles, bathtubs, sinks and taps as
well as doors, door handles etc. By selecting “basic” you are implying that you will
be buying PC items where cost is of higher concern than quality or style. Selecting
“standard” implies that quality is as important as cost, but style is less important
than either. If you select “luxury” you are implying that style and quality
are more important than cost.
cost per-square-foot: indoor areas $
garage $
decks, verandahs & patios $
master bedroom  
ensuite bathroom  
dining area  
walkin closet  
living area  
bedroom 2  
home office / study  
bedroom 3  
rumpus room / play area  
bedroom 4  
main bathroom  
other bedrooms  

2nd bathroom  
other bathrooms  

porches & patios  
other indoor areas or rooms  

* The total calculated indoor area will include a minimum of 10% for
circulation“; i.e., areas such hallways, entrances and stairways. Select 20% or 25% if you want your
house to feel spacious.

 indoor area (includes circulation space)

 outdoor areas


 total area (in square feet)

 indoor area (includes circulation space)

 outdoor areas


 total cost



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