Two-way labour calculator: given total hours + target duration → operatives needed,
or given operatives + pattern → duration needed. Includes productivity factor and optional overtime.
For design guidance only. Always verify with a qualified planner / estimator.
About this resource / labour loading calculator
This free resource and labour loading calculator works two ways: enter your total work hours and a target duration to find the number of operatives required, or enter the operatives available to find the duration needed. It applies a productivity factor and lets you add overtime, so the answer reflects a realistic working week rather than raw hours on paper. It is built for UK building-services engineers, estimators and contractors sizing a crew at tender or planning stage, and the result can be copied, exported to CSV, printed to PDF or shared as a link.
How the labour loading is calculated
Gross weekly hours per person are the days per week multiplied by hours per day, plus any overtime per week. That figure is then multiplied by the productivity percentage (85% is offered as a typical default to account for breaks, access and coordination) to give effective hours per person per week. In “find operatives” mode the calculator divides total work hours by effective weekly hours multiplied by the target weeks, then rounds up to whole operatives. In “find duration” mode it divides total work hours by effective weekly hours multiplied by the operatives available. The footnote frames the output as tender-stage resource planning per NRM2 §5 and the CIOB Code of Estimating Practice, and advises splitting work into packages where coordination losses are significant.
Frequently asked questions
What does the productivity percentage do?
It scales gross weekly hours down to effective hours, recognising that not every paid hour is productive. The calculator suggests 85% as a typical value to allow for breaks, access and coordination, but you can set your own.
Can it work out the programme duration as well as the crew size?
Yes. Switch the mode to “find duration required”, enter the operatives available, and it returns the weeks needed along with approximate work days and calendar days.
Is the operative count exact or rounded?
The breakdown shows the exact figure and the rounded-up whole number of operatives, since you cannot allocate a fraction of a person. Treat it as a tender-stage estimate and always verify with a qualified planner or estimator.