Construction inputs: how to break a m² of plaster or a m³ of column into hours, material and waste
Construction inputs are everything that goes into producing one unit of work: hours of tradespeople and helpers, material including waste, and equipment. When you break a m² of plaster or a m³ of column down into its inputs, you see where the price comes from, and you can check whether a price you received is reasonable. I have experience in breaking prices down into inputs, starting with the cost analyses I prepared in my final project in construction management, and in every tender since.
Input, output and productivity: the same number from both directions
An input is how many working hours one unit needs, for example 0.25 hours per m². Output, also called productivity, is the inverse: how many units are done in an hour, in the same example 4 m² per hour. Both numbers say the same thing, and whoever calculates a schedule or a price needs to know which of the two he is using, because a mistake in the direction multiplies the result several times over.
In the industry the word "inputs" has two more meanings. The construction inputs index is the price index to which building contracts are linked, covered on the page index linkage and VAT. Input tax is the VAT a contractor pays on purchases and offsets against the VAT he collects. Three meanings, one word, so it is worth always writing what you mean.
A sample table of construction inputs, from my final project
The table sums up inputs I used in the cost analyses of my final project. They are an illustration: they change with every project, crew and method.
| Work | Labour input | Material waste | Note |
|---|---|---|---|
| Internal plaster, two coats | 0.25 plasterer hours and 0.25 helper hours per m² | 25% | Average thickness 1.5 cm |
| Internal floor tiling | 0.4 tiler hours and 0.4 helper hours per m² | 7% | Mortar bed about 2 cm thick |
| Concrete column 22/40 | One formwork carpenter hour per m² of formwork; 1.6 pouring hours per m³ | 4% | Timber cutting waste: 10% |
| Timber formwork | Ten uses per board | 10% | The cost of the timber is divided by the number of uses |
Alongside the inputs, the amount of rebar in each element is measured in kg per m³ of concrete. The ranges are for illustration only; the real quantity comes from the reinforcement drawings.
| Element | Range |
|---|---|
| Ground slabs and suspended slabs | 80–100 |
| Walls | 90–110 |
| Columns | 110–130 |
| Beams | 100–120 |
| Piles | 80–100 |
| Raft and foundations | 100–110 |
An example: one m² of internal plaster, from inputs to quantity
An average thickness of 1.5 cm is 0.015 m³ of plaster per m² of wall. With waste of 25%, and with the method of dividing by the part that remains, you get 0.015 divided by 0.75, that is 0.02 m³ per m². On 1,000 m² of walls, that is 20 m³ of ready-mixed plaster. The labour: 1,000 times 0.25, that is 250 plasterer hours and 250 helper hours. With a crew of two plasterers and two helpers at 9 hours a day, the work takes about 14 days. If you multiply by 1.25 instead of dividing by 0.75, you get 0.01875 m³ per m², almost 7% less material in the order. The difference is small on one m² and noticeable in a whole building.
An example: how much formwork there is in one m³ of column
A column with a 22 by 40 cm section: to hold one m³, it has to be 1 divided by 0.088, that is 11.36 metres long. The perimeter of the section is 1.24 metres, so the formwork area is 1.24 times 11.36, that is about 14.1 m² of formwork per m³. For comparison, a slab 20 cm thick: one m³ is 5 m² of slab, and only about 5 m² of formwork. This is one of the reasons a m³ of column costs much more than a m³ of slab, even when the concrete is the same. The link between measurement and price is on the page physical quantity, quantity in the bill of quantities (BOQ) and quantity to order.
From inputs to price: how to check a quote for one m² of plaster
To check a price, you multiply each input by its price. The numbers here are for illustration only, and they are not market prices; every contractor puts in his own prices.
| Component | Input per m² | Illustrative unit price | Shekels per m² |
|---|---|---|---|
| Plasterer | 0.25 hours | 100 per hour | 25 |
| Helper | 0.25 hours | 60 per hour | 15 |
| Ready-mixed plaster | 0.02 m³ | 400 per m³ | 8 |
| Scaffolding and equipment | – | – | 4 |
| Direct cost | 52 | ||
| Overheads and profit, 15% | 8 | ||
| Price per m² | 60 |
If a quote comes in at 35 shekels per m², it is lower even than the direct cost in the example. There are three possible explanations: a thinner coat than the specification requires, an especially fast crew, or a price that will come back later as a variation. One question to the contractor, "how many hours do you allow per m²?", clears it up quickly.
The third type of input is equipment: a crane, a concrete pump, scaffolding and a mixer. It is measured in equipment hours per unit, or in equipment days for the whole project, and then it goes into the overheads. Some pricing methods also have a fourth type, subcontractors, who are priced at an all-in rate per unit.
Why this matters to you: a price that does not break down into inputs cannot be checked. When you know how many hours and how much material go into one m², you see quickly whether a quote is too low, in which case it will come back as a variation, or too high. How this connects to the schedule is on the page construction schedule.
Inputs are derived from a quantity takeoff: how many working hours, how much material and how many equipment days for each unit. A quantity surveyor who holds this data can check whether a quote fits the scope of the work.
Frequently asked questions
What is the difference between inputs and price?
Inputs are the quantities: hours, material and equipment per unit. The price is the inputs times market prices, with overheads and profit on top, as explained on the page site overheads.
Where do construction inputs come from?
From catalogues of guideline values and standard times, from professional literature, and mainly from contractors' experience on site. In finishes such as plaster and tiling, it is worth cross-checking with a finishes quantity takeoff.
Why divide by the waste rather than multiply?
Because waste of 25% means that a quarter of the material bought is lost. For 0.015 m³ to stay on the wall, you have to buy 0.015 divided by 0.75. Multiplying by 1.25 comes close, but slightly under.
Who can break a quote down into inputs for me?
A quantity surveyor for construction projects who has worked in pricing at contractors. It is the basis of any comparison of quotes.
Have a project? Tell me briefly what the project is and what already exists. When the project is a good fit, I usually reply with focused questions and a written quote.
Contact me for a quote* Created with AI for marketing, for illustration only. Not reviewed by Yaakov Avital and not professional advice. Every project must be checked on its own by a professional quantity surveyor and an engineer.