Last reviewed 16 Sept 2026 · 8 min read
What is an estimate?
An estimate is a calculation of the probable cost of a project before construction, prepared from drawings, specifications and current rates.
Purposes
- Determine the approximate cost for deciding feasibility and obtaining administrative approval and financial sanction.
- Arrange funds and budget allocations.
- Invite tenders and compare bids (bill of quantities).
- Plan quantities of materials, labour and equipment and schedule procurement.
- Control expenditure during execution; prepare valuation of existing properties.
Data required
- Drawings — plans, elevations, sections, detailed drawings.
- Specifications — general and detailed (quality of materials and workmanship).
- Rates — schedule of rates (e.g. CPWD/State PWD DSR) or analysed rates for items.
- Site information — soil, access, leads for materials, local conditions.
Approximate (preliminary) estimates
Prepared quickly for feasibility and administrative approval, before detailed drawings exist.
| Method | Basis | Formula / remarks |
|---|---|---|
| Plinth area method | Cost per unit plinth area of similar buildings in the locality | Cost = plinth area × plinth area rate; plinth area measured at floor level including external walls; separate rates for different floors/specifications |
| Cubic content (cubical) method | Cost per unit volume of similar buildings | Cost = volume × cubic rate; volume = plinth area × height (e.g. from floor/plinth level to top of roof) — better than plinth area for buildings of different heights |
| Service unit (unit base) method | Cost per unit of service provided | e.g. per bed (hospital), per student (school), per seat (theatre), per classroom, per km (road), per tonne of storage |
| Typical bay method | Cost of one typical bay (between column lines) in repetitive buildings | Cost = cost of one bay × number of bays (+ adjustments for end bays) — factories, warehouses, halls |
| Approximate quantity (bill) method | Approximate quantities of major items (e.g. per running metre of wall including foundation, superstructure, finishes) × rates | More accurate than area methods |
Additions to building cost (commonly allowed as percentages of building cost when detailed estimates are not available): water supply and sanitary installations, electrical installations, and other services (often of the order of several per cent each), plus contingencies and supervision charges.
Detailed estimate (item rate estimate)
Prepared from complete drawings and specifications for technical sanction and tendering.
Steps
- Details of measurements — each item of work is measured (number, length, breadth, height/depth) from drawings and quantities computed as per standard modes of measurement.
- Abstract of estimated cost — quantities of each item multiplied by rates to get amounts; items grouped (earthwork, concrete, masonry, finishing etc.).
- Additional provisions on the total:
- Contingencies — for unforeseen items and minor variations (commonly about 3–5%).
- Work-charged establishment — wages of staff employed specifically for the work (e.g. work supervisors, chowkidars) (commonly around 1.5–2%).
- Tools and plant, quality control, petty supervision, centage charges (departmental charges for design and supervision in deposit works) as per departmental rules.
- Report explaining the need, design basis, specifications, rates adopted, cost and sources of funds.
- Drawings and specifications attached.
Other types of estimates
| Estimate | Purpose |
|---|---|
| Revised estimate | A detailed estimate prepared again when the sanctioned estimate is likely to be exceeded beyond permissible limits (as per departmental rules), or when there are material deviations from the original proposal — requires fresh sanction |
| Supplementary estimate | For additional works found necessary during execution that were not part of the original estimate |
| Annual repair (maintenance) estimate | For routine yearly maintenance — whitewashing, painting, minor repairs — often a small percentage of the capital cost |
| Special repair estimate | For major repairs beyond routine maintenance (e.g. re-roofing) |
| Complete estimate | Total cost of a project including land acquisition, buildings, services, roads, compound walls, establishment, etc. |
| Quantity estimate (quantity survey) | Only quantities of all items (used in tender documents as the bill of quantities) |
| Project estimate | Consolidated estimate for a large project with sub-works |