What does it mean?
A prime cost sum is an allowance for a specified cost component, often the supply of an item whose final selection is unresolved. Its exact meaning depends on the contract and pricing documents. Installation, delivery, attendance, wastage and contractor additions may be handled separately. Always read the item description before treating the allowance as a complete installed cost.
In practice
A tile supply allowance of 30 per m² for 20 m² produces a base supply allowance of 600. Adhesive, labour, cutting waste and other additions may sit outside that amount.
Keep in mind
For a project record, note the document reference, revision and agreed measurement or contractual basis beside the quantity. Keep assumed information visibly separate from confirmed information. If two parties use different definitions or inclusions, resolve that difference before comparing amounts. These explanations are general estimating context; the wording of the applicable contract and its administration process must be checked for the particular job.