Every paper that follows a work — the DNIT, the agreement, each RA bill, the deviation statement, the completion report — leans on the detailed estimate prepared at the very beginning. When the estimate is sound, the rest of the file more or less writes itself. When it is careless, we spend the next two years explaining it. In our office we treat the detailed estimate as the one document worth slowing down for, and this note sets out how we build one, in the order the work actually happens.
What a detailed estimate must establish
A detailed estimate is not a guess dressed up in tables. It has to establish four things to the satisfaction of the sanctioning authority. First, what exactly is proposed — every component of the work resolved into items with proper nomenclature, so the specification is beyond argument. Second, how much of each item — quantities taken off from dimensioned drawings, not from memory of a similar work. Third, what it should cost — each quantity priced at the rate of the schedule of rates in force, with non-schedule rates separately justified. Fourth, that the provision is complete — dewatering, disposal, scaffolding-dependent items and site-specific enabling works included now, not discovered at the first running bill.
We remind our juniors that the estimate is also the yardstick everything later is judged against: deviations are deviations from this document. An estimate that cannot be retraced cannot defend a deviation statement either.
Drawings and site data to gather
Before a single dimension is booked, we collect the inputs and record their references on the cover page:
- Working drawings — plans, sections and elevations at a usable scale, foundation details, and structural drawings for all RCC members. If the drawings are still "architectural only", the estimate is premature.
- Site levels — a grid of spot levels over the plot, because earthwork quantities computed from an assumed formation level rarely survive the first joint measurement.
- Soil information — classification for excavation items (ordinary soil, hard soil, rock requiring blasting or chiselling), and the water table where dewatering may arise.
- Leads and approach — distance to the borrow area, to the disposal point for surplus earth and malba, and the condition of the approach road, since carriage items depend on all three.
- Services at site — whether water and electricity are available departmentally or the contractor must arrange them; this decides both items and add-ons later.
- The SoR edition — note the schedule of rates edition and the correction slips in force on the date of preparation. This single line saves an astonishing amount of audit correspondence.
Measurement discipline — the IS 1200 spirit
The IS 1200 series lays down the method of measurement trade by trade, and its spirit can be put in one sentence: measure the work the way it will be paid for. The estimate's take-off must follow the same measurement rules that the measurement book will follow during execution, otherwise the estimate and the bills speak two different languages.
In practice that means a few habits:
- Book dimensions in a fixed sequence — length, then breadth, then height or depth — so a checker knows what each figure is without asking.
- Respect the degree of accuracy the measurement rules prescribe for each trade; do not carry earthwork to the millimetre while rounding steel to the quintal.
- Apply the deduction conventions for openings exactly as the governing rules state them. Most schedules ignore openings below a stated size, deduct larger ones fully or partly, and treat the two faces of a plastered wall differently depending on how the frame sits. The specific thresholds vary between organisations — what matters is to look them up in the rules that govern your schedule and apply them the same way on every wall, in the estimate and in the MB alike.
- Measure work that will be hidden — foundation concrete, waterproofing beneath the floor — as separate, clearly labelled entries, because at site these are recorded before covering and the estimate should mirror that.
The test we apply: could an independent JE, given only the drawings and the measurement rules, reproduce our quantities within rounding? If yes, the estimate is defensible. If no, it is an opinion.
Building the details of measurement
The details of measurement (DoM) is the working heart of the estimate — one sheet per item, columns for description, number, length, breadth, depth and quantity. Our conventions:
- Group items by sub-head in construction order — earthwork, concrete, RCC, masonry, wood and steel work, flooring, finishing, services — so the estimate reads like the work will be built.
- Enter deductions as negative lines under the same item, each labelled ("deduct: door D1, 2 nos"), never by silently shrinking a dimension. The audit trail is the whole point.
- Note the source of every dimension — drawing number and grid line — in the remarks column. Six months later nobody remembers which revision the 3.45 came from.
- For walls and footings, choose the centre-line method or the long-and-short-wall method and stay with it throughout; mixing the two on one building is how corners get counted twice.
A printable sheet in this format is on our measurement-sheet proforma page, and a spreadsheet version is available as a CSV template.
Schedule items vs non-schedule items
Our first preference is always a schedule item: its rate is already analysed, sanctioned and beyond debate. The discipline is to use the item's nomenclature as printed — if the schedule item says 20 mm plaster in a given mortar and the drawing shows something else, we do not shoehorn; we find the right item or raise a new one.
When no schedule item genuinely fits, we frame a non-schedule (NS) item, and its rate must be justified, not asserted:
- Write a complete nomenclature — material, dimensions, mode of measurement and what the rate includes — as carefully as a schedule entry would.
- Prepare an analysis of rates: material constants and labour constants for the operation, priced at prevailing market rates supported by quotations kept on record, plus carriage where it applies.
- Add the contractor's profit and overheads at the percentage your organisation's rules allow.
- Put the analysis up for approval by the authority competent to sanction such rates, and file it with the estimate.
An estimate carrying many NS items is a signal to pause — either the schedule edition is badly out of date or the design has drifted from standard practice, and the sanctioning authority will ask which.
Add-ons: contingencies, water, electricity, cess
Below the sub-total of measured items come the percentage add-ons, and here the only safe rule is: take the percentages from your organisation's current orders, not from the last estimate you copied. The usual heads are:
- Contingencies — a small percentage for petty unforeseen items that do not merit their own line.
- Water charges — where the department supplies water for the work, recovered or provided for at the prescribed percentage.
- Electricity charges — likewise, where power for construction is supplied departmentally.
- Labour cess — the levy on the cost of construction under the building-workers welfare legislation, at the rate notified for your state.
- Other heads some organisations prescribe — quality-assurance charges, an escalation provision on long-duration works, and charges for temporary works.
Each add-on is shown as its own line on the abstract, with the percentage and the base it is applied to stated explicitly. A lumped "add 5% misc." is an invitation to objection.
The abstract of cost
The abstract of cost is the estimate's public face: one line per item — serial number, description, quantity, unit, rate and amount — grouped by sub-head with sub-totals, then the add-ons, then the grand total rounded per office convention. Two properties make an abstract sound:
- Traceability — every quantity on the abstract is the closing figure of a DoM sheet, transferred without adjustment. If a quantity needs revising, revise the DoM and let the abstract follow.
- Consistency — the unit on the abstract matches the unit of the schedule item, and the rate matches the SoR edition named on the cover page, correction slips included.
Before signing, we run one mechanical check both ways: every DoM sheet has a line on the abstract, and every abstract line has a DoM sheet. A starter layout is available as an abstract-of-cost CSV template.
Common pitfalls
The mistakes we see repeatedly are few, and all preventable:
- Unit mismatch — a quantity computed in m³ against an item paid in m² (or the reverse), classically where a thickness-inclusive item sits next to an area-based one; and rates read from schedules priced per 10 m² or per quintal but applied per unit. Check every line's unit against the schedule, not against the neighbouring line.
- Double deduction — deducting an opening from the masonry and then again from both plaster faces when the rules say otherwise, or deducting both the lintel and the opening over the same volume. One deduction rule, applied once.
- Forgetting lead and lift — the base excavation and carriage items cover an initial lead and lift only; extra lead to the actual disposal point and extra lift below the initial depth are separate items, and omitting them understates earthwork on every deep foundation.
- Stale SoR edition — an estimate prepared over months and put up against a schedule that has since been revised. Re-verify the edition and correction slips on the day the estimate is signed, and say so on the cover.
- Wholesale copying — starting from last year's estimate for a "similar" building and inheriting its site, its leads and its mistakes.
- Missing enabling items — dewatering, shoring and strutting, barricading, site clearance and anti-termite treatment: cheap to provide now, expensive to regularise later as extra items.
Once sanctioned, the estimate flows onward — its quantities seed the DNIT schedule, the agreement freezes the rates, and every running-account bill and deviation statement is checked against it. The hours spent getting the take-off right are repaid at every one of those stages. For the arithmetic along the way, our free quantity calculators and material consumption norms cover the routine conversions.