Types of estimates in construction: plinth area, cube rate and detailed
Published 5 Oct 2026
There are two families of construction estimate. Approximate estimates (plinth area, cube rate, approximate quantity) give a budget figure from limited information. The detailed estimate measures every item from drawings and prices it from a schedule of rates. Use approximate estimates to decide whether to build, and the detailed estimate to tender, contract and control cost.
The types at a glance
| Estimate | Based on | Formula | Accuracy | Typical stage |
|---|---|---|---|---|
| Plinth area | Covered area at floor level | Plinth area x plinth area rate | Rough | Idea, loan or budget check |
| Cube rate | Volume of the building | Plinth area x height x cube rate | Better than plinth area | Multi-storey or varying heights |
| Approximate quantity | Main items from thumb rules | Item quantities x rates | Moderate | Early design, before drawings are final |
| Detailed | Item-by-item measurement from drawings | Quantity x rate for every item | Highest | Tender, contract, work order |
| Revised | An approved estimate that has been exceeded | Original plus changes | Depends | During construction |
| Supplementary | Additional work not in the original scope | Extra items only | Depends | During construction |
Plinth area estimate
Plinth area is the covered area of a building measured at floor level, walls included. Open terraces, open courtyards and open parking are not part of it. The plinth area rate is taken from the cost of a similar building, with similar specification, in the same locality.
Plinth area estimate = plinth area x plinth area rate
Example with assumed figures: a 1,200 sq ft plinth area at Rs 1,800 per sq ft gives Rs 21.6 lakh. Treat the rate as an input you must source locally. Published 2026 ranges for standard houses in India sit roughly between Rs 1,500 and Rs 2,800 per sq ft depending on city and finish.
Cube rate estimate
A cube rate estimate uses volume instead of area. Height is measured from floor level to the top of the roof, and the foundation, plinth and parapet above the roof are left out.
Cube rate estimate = plinth area x height x cube rate
Using the same house: 1,200 sq ft x 10 ft = 12,000 cft. At an assumed Rs 180 per cft, that is Rs 21.6 lakh. The method suits multi-storey buildings and buildings with different storey heights because height changes the answer.
Approximate quantity estimate
This method estimates the main items (earthwork, concrete, steel, masonry, plaster, flooring) from thumb rules and prices them. It sits between a per-sq-ft guess and a full measurement.
Detailed estimate
A detailed estimate is prepared item by item from working drawings. It normally comes with a report, general and detailed specifications, drawings, measurement and calculation sheets, and the analysis of rates. It is the document used for technical sanction, tendering and work orders.
To prepare one, follow how to make a BOQ from drawings, measure with the centre line or long wall-short wall method, apply deduction rules and price items using rate analysis. To skip the manual work, upload drawings to the Detailed Estimate.
Revised and supplementary estimates
A revised estimate is needed when the sanctioned cost is going to be exceeded. A supplementary estimate covers additional work that was not in the original scope. Neither replaces the detailed estimate. Both build on it.
Plinth area, built-up area and carpet area
The area you plug into an estimate decides the answer, and these terms are often mixed up.
| Term | What it measures | Rule of thumb |
|---|---|---|
| Carpet area | Usable floor area inside the walls | Roughly 70 - 75% of plinth area |
| Built-up area | Carpet area plus wall thickness plus balconies and utility areas | Usually 10 - 20% more than carpet area |
| Plinth area | Covered area at floor level, walls included (BIS definition) | Close to built-up area for most houses |
| Super built-up area | Built-up area plus a share of common areas | A marketing figure for apartments, not for estimating a house |
For an independent house, estimate on plinth or built-up area. Never feed carpet area into a per-sq-ft rate that was derived from plinth area, or the estimate will come out too low.
Which estimate should you use?
| Your situation | Use |
|---|---|
| Checking whether a plot and budget are realistic | Plinth area estimate |
| Comparing storey heights or a multi-storey option | Cube rate estimate |
| Early design, client budget, no final drawings | Approximate quantity estimate |
| Tender, contractor quote, work order, bill checking | Detailed estimate |
| Cost has crossed the sanctioned amount | Revised estimate |
Move from a rough number to a real one
Start from the ready-filled example in the online BOQ editor for a budget, then upload working drawings to the Detailed Estimate when you need quantities measured from the drawings. For the cost-per-sq-ft view, read how to estimate house construction cost in India.
Frequently asked questions
What are the main types of estimates in civil engineering?
Preliminary or approximate (plinth area, cube rate, approximate quantity), detailed, revised, supplementary and annual repair estimates.
What is the difference between plinth area and carpet area?
Plinth area includes the thickness of walls and is measured at floor level. Carpet area is only the usable floor inside the walls, so it is smaller.
Which estimate is the most accurate?
The detailed estimate, because it measures each item from drawings. Cube rate is generally more accurate than plinth area.
Is a BOQ the same as a detailed estimate?
They are closely related. A BOQ lists items, units and quantities. A detailed estimate also carries rates, specifications and rate analysis. See BOQ vs BOM vs abstract of cost.