Construction Rate Analysis: Material Constants, Labour Productivity Norms, Shuttering Factor and Testing Cost

A unit rate in a BOQ is only as reliable as the analysis behind it. Two estimators can price the same cubic metre of concrete 15–20% apart — not because markets differ, but because one used realistic dry-volume factors, wastage and labour output, and the other copied an old rate and added a percentage. Rate analysis is the discipline that closes this gap: it breaks every item into the quantities of material, labour, plant and testing it consumes, prices each component at current market rates, and adds overheads and profit transparently.

This guide explains how a professional rate analysis is built, the standard material constants every Quantity Surveyor should know, labour productivity norms, the shuttering factor that most estimators get wrong, and how testing costs are converted into a per-unit charge.

All constants and outputs below are typical engineering values for estimating. Site conditions, specifications and local productivity change them. Always calibrate with your own project records.

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STEP 011. What a Rate Analysis Contains

Every analysed item follows the same structure, regardless of trade:

The analysis is prepared for a convenient batch quantity (for example 100 Cft, 10 m³ or 1 m³) and then divided down to the unit rate. The batch size does not change the rate — it only makes the arithmetic readable.

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STEP 022. Concrete: Dry Volume and Mix Constants

Wet concrete occupies less volume than the loose dry materials that make it, because fine particles fill voids and water consolidates the mix. The standard estimating allowance is:

Dry volume = Wet volume × 1.54 (some practitioners use 1.52–1.57)

For a nominal mix of ratio 1 : s : a (cement : sand : aggregate):

• Cement volume = Dry volume × 1 / (1 + s + a)
• Sand volume = Dry volume × s / (1 + s + a)
• Aggregate volume = Dry volume × a / (1 + s + a)
• 1 bag of cement (50 kg) ≈ 1.25 Cft (0.0347 m³)

Indicative quantities per 100 Cft of wet concrete:

Strength classes for nominal mixes are approximate. For structural work, a designed mix verified by trial batches and testing should always govern.

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STEP 033. The Shuttering Factor — Converting Cft of Concrete into Sft of Formwork

Concrete is priced per Cft or m³, but formwork is measured by contact area (Sft or m²). The link between them is the shuttering factor: the formwork area required per unit volume of concrete. It depends entirely on the element's geometry.

Slab Only the soffit is formed. For a 6" (0.5 ft) slab: Factor = 1 / 0.5 = 2.0 Sft per Cft

Column All four faces are formed. For a 12" × 12" column, per 1 ft height: Perimeter = 4 Sft, Volume = 1 Cft → Factor = 4.0 Sft per Cft

Suspended / roof beam (with slab) For a 12" × 18" beam under a 6" slab, only the 12" drop below the slab is formed on the sides:

• Sides only (bottom counted with slab): 2 × 1.0 = 2 Sft per 1 Cft drop → 2.0 Sft/Cft
• Sides + bottom: 2 + 1 = 3 Sft → 3.0 Sft/Cft

Plinth beam Three faces (two sides + bottom or two sides + top shutter, depending on method). For a 9" × 18" plinth beam: sides 2 × 1.5 = 3.0 Sft, plus width 0.75 Sft = 3.75 Sft on a volume of 1.125 Cft → ≈ 3.33 Sft/Cft

Multiple sizes Real projects have several column and beam sizes. The professional approach is to calculate the factor for each size and take the mean (or a quantity-weighted mean when quantities are known). This one step typically corrects formwork cost errors of 30–50% that come from using a single "blanket" factor.

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STEP 044. Testing Cost as a Per-Unit Charge

Testing is a real, recoverable cost that is often forgotten in rate analysis. It is converted into a nominal per-unit charge:

Testing cost per Cft = Lab charge per set ÷ Lot size in Cft

Example: one set of 3 cylinders (ASTM C39) tested per 50 m³ lot at an external laboratory for 3,500 per set:

• 50 m³ × 35.3147 = 1,765.7 Cft
• 3,500 ÷ 1,765.7 ≈ 2.0 per Cft

The same logic applies to rebar tensile/bend tests (per tonne lot) and brick compressive strength tests (per number of bricks). Small per unit — but over a large structure it is a significant, auditable amount.

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STEP 055. Labour Productivity Norms

Labour is analysed by gang output per day. Indicative norms for estimating (8-hour day, average site conditions):

Your own DPR records are the best source of productivity. A rate analysis built on actual site outputs is far more defensible than one built on generic tables.

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STEP 066. Common Material Constants

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STEP 077. A Worked Outline: RCC 1 : 1.5 : 3 Roof Slab (6"), per 100 Cft

1. Materials — 22 bags cement, 42 Cft sand, 84 Cft aggregate, water; formwork material for 200 Sft (factor 2.0) depreciated over reuses.
2. Labour — concrete gang for mixing, placing, vibration and curing; carpenter gang for fixing and stripping 200 Sft of formwork.
3. Testing — 100 Cft × ≈ 2.0 per Cft (cylinder testing per 50 m³ lot).
4. Tools & Plant — mixer, vibrator, small tools (as hire or a percentage of labour).
5. Overheads & profit — e.g. 15% on sub-total.
6. Taxes — as applicable.
7. Unit rate — Total ÷ 100 = rate per Cft (or × 35.3147 for per m³).

The item description is then written to match exactly what was analysed — mix, element, thickness, formwork and testing included — so the BOQ rate and the BOQ wording never contradict each other.

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STEP 088. Why Rate Analysis Fails in Practice

• Copied old rates with a blanket percentage increase instead of re-pricing components.
• One shuttering factor used for slabs, beams and columns alike.
• Testing, curing and cleaning omitted, then claimed later as "extra".
• No link between materials across items — cement priced at one rate in concrete and another in plaster.
• Description and analysis mismatch — the BOQ says "including formwork" but the analysis has none.

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STEP 099. Do It in Minutes with Rate Analysis Pro

CM PRO's free Rate Analysis Pro applies everything in this article automatically:

• Select Trade → Concrete Class → Element, and the tool calculates material quantities with the 1.54 dry-volume factor.
• Enter one or more column, beam or slab sizes — it computes the mean shuttering factor and adds formwork material and labour.
• Testing cost per Cft is calculated from your lab rate and lot size, with the formula printed under the analysis.
• A rule-based item description is generated from your selections and remains editable.
• Choose your own batch volume, then print a clean A4 sheet with a signature block.
• Signed-in users can create a project and add each analysis directly to a BOQ, with editable quantities and drag-to-reorder rows.

Related free resources:

• Measurement Sheet format — record quantities that feed your BOQ.
• Construction calculators — bricks, plaster, paint, tiles and concrete volumes.
• Price Escalation guide — adjusting your rates when markets move.
• Concrete strength science — why mix and curing assumptions matter.

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STEP 10References

• ASTM C39 — Standard Test Method for Compressive Strength of Cylindrical Concrete Specimens.
• ASTM C31 — Standard Practice for Making and Curing Concrete Test Specimens in the Field.
• ASTM C33 — Standard Specification for Concrete Aggregates; ASTM C150 — Portland Cement.
• ACI 347 — Guide to Formwork for Concrete.
• RICS — New Rules of Measurement (NRM2), detailed measurement for building works.
• CESMM4 — Civil Engineering Standard Method of Measurement.

Values in this article are estimating guidance, not code-mandated figures. Verify specifications and calibrate productivity against your own project data.