Construction Glossary
Gross Internal Area
Also known as GIA
Definition
Gross internal area, or GIA, is the floor area of a building measured to the inside face of the external walls, including internal walls, columns and circulation. It is a standard way of measuring buildings used for cost rates, comparisons and valuations. RICS publishes the measurement rules that define it. Costs per square metre are usually quoted against GIA.
GIA measures everything inside the outer walls across all floors, including corridors, stairwells, internal walls and plant areas, but excluding the thickness of the external walls themselves. It gives a consistent figure for the size of a building.
Because it is a recognised standard, GIA is the area most early cost rates are based on, which makes it the natural unit for budgeting and benchmarking.
Why it matters
Early budgets and viability checks live or die on the floor area you start from. Use a loose or wrong GIA and your cost per square metre carries the error straight into the budget. A correct GIA gives developers a sound base for budgeting and comparing schemes.
We measure gross internal area from your drawings so your cost plans and rate based estimates start from a reliable floor area.
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