What does it mean?
A cost plan organises the expected project cost so it can be tested and managed as the design develops. It records scope, quantities, rates, allowances and exclusions at an appropriate level of detail. It is more than multiplying a floor area by a benchmark: that multiplication can be a starting check, but it does not capture every project-specific requirement.
In practice
A 120 m² building at an assumed 2,000 per m² indicates 240,000 on that basis. The estimator must establish whether external works, fees, taxes, risk and other items are included before treating it as a project budget.
Keep in mind
For a useful comparison, record the currency, pricing date, scope and exclusions alongside the amount. Separate measured quantities from unit prices so you can identify whether a change comes from design or pricing. Use project-specific quotations where available, and distinguish an illustrative allowance from a confirmed cost. The calculators show arithmetic relationships; they do not supply current market rates, tax advice or a complete project budget.