Suppose the crew costs the same tomorrow as it does today, but it completes less work. The missing output has not made the people or plant cheaper. Their cost is spread over fewer units.
That is the relationship behind a productivity rate, and it is often more useful than arguing over the final price per cubic metre. First establish crew cost over a defined period. Then establish what it can produce over that same period.
Take a crew costing £1,600 per day. Its baseline output is 25 m³ per hour over an eight-hour shift. If 80% efficiency is applied, effective hourly output is 20 m³. Daily production is therefore 160 m³ and crew cost is £10 per m³.
Daily crew cost is fixed in this illustration. Lower output raises the cost of each cubic metre.
Find out what the baseline already contains
An efficiency factor needs a meaning. Does 25 m³ per hour describe continuous productive operation, or is it an observed average from a working shift that already includes delays? Applying another reduction to a shift average may allow for the same lost time twice.
Write down the convention before using the percentage. If breaks, access restrictions or waiting for deliveries are already reflected in the baseline, explain which additional effect the adjustment represents. A percentage chosen because the result feels optimistic is hard to review later.
Move between hours, days and units carefully
For the 1,200 m³ exercise, divide scope by effective daily production: 1,200 ÷ 160 = 7.5 working days. Multiplying 7.5 days by £1,600 gives £12,000. The alternative route, 1,200 m³ × £10 per m³, gives the same total.
Both routes assume the crew can be paid or allocated for half a day. If the commercial arrangement requires eight full days, the total becomes £12,800. Neither convention should be hidden. The training answer uses fractional days because the question explicitly supplies that basis.
- 25 m³ per hour baseline
- At 80%: 20 m³ per hour
- Over 8 hours: 160 m³ per day
- £1,600 ÷ 160: £10 per m³
Efficiency is applied once. The example assumes fractional-day payment and excludes mobilisation and disposal.
Build the crew before pricing its output
Another exercise starts with three operatives at £23 per hour and a supervisor at £32 per hour. The combined cost is 3 × 23 + 32 = £101 per hour. Over eight hours that is £808. At 8 m³ per hour, labour costs £12.625 per m³.
Do not divide £101 per hour by 64 m³ per day. Those numbers describe different periods. Either divide hourly cost by hourly output, or daily cost by daily output. Both valid routes return £12.625 per m³.
More resources do not guarantee more output
A second excavator may have little effect if one access point limits truck movements. An extra placing crew may wait for the same concrete deliveries. Adding resources can raise the cost while leaving output unchanged.
A sensible review starts with the controlling operation. Ask what limits production, how the work is sequenced and whether supporting resources can keep up. The answer might be a better delivery pattern rather than a larger crew.
When an exercise answer is wrong, trace the units before changing the arithmetic. When a commercial estimate looks wrong, inspect the work method as well. A rate can be mathematically correct and still describe a job that cannot be delivered in the way assumed.