算BuildCalc

Construction Duration Calculator

Quantity × labour norm ÷ crew gives the days you need.

Quick answer

With the default inputs: Quantity 1000 · Labour norm 0.5 man-days/unit · Crew size 20 persons etc.Calendar duration 32 days

Edit the inputs below to recalculate.

Inputs

Must match the unit of the labour norm
man-days/unit
Man-days per unit, from the norm handbook
persons
shifts
2 for double shifts, though productivity drops
%
Sickness and leave included, usually 90-98%
%
After rain, wind and stoppages — usually 75-90%

Result

Calendar duration
32days
Total man-days500.0man-days
Daily man-days19.00man-days/d
Working days27days
Calendar days32days
In months1.1months
Output per day37.0units/d
Crew for 30 days18persons
With 20% float39days

Two figures must not be confused: working days are days actually worked, calendar days include rain, stoppages and rest — and only the latter goes to the client and the programme. Calendar = working ÷ workable ratio. Note that adding people is not linear: work fronts are limited, efficiency collapses past a sensible crew size, and night shifts run at only 70-85% of day output. This tool is linear, so add 10-20% in practice.

Formula

Total man-daysT = quantity × labour norm
Daily capacityC = crew × shifts × attendance
Working daysD = ⌈T ÷ C⌉
Calendar daysD = ⌈working days ÷ workable ratio⌉
Crew for a targetN = T ÷ target ÷ (shifts × attendance)
1000 units at 0.5 man-days, 20 workers, one shift, 95% attendance and 85% workable: 500 man-days, 19 per day, 27 working days, 32 calendar days — 18 workers to finish in 30 days.

How to work it out

  1. Align units first: the norm is in labour days per unit, so the quantity must use the same unit.
  2. Total labour days = quantity × time norm. A 1000 m² wall at 0.5 labour days per m² is 500 labour days.
  3. Calendar days = total labour days ÷ (crew size × shifts per day × attendance × productive-day ratio).
  4. The productive-day ratio covers rain, wind, heat and inspections: 75-85% outdoors and 90-95% indoors.
  5. Sanity-check: when the answer is far shorter than experience, either the crew will not fit the work face or the norm is optimistic.

Where it goes wrong

Material and cost

Programme shows up in indirect cost: management, temporary works, plant hire and finance all accrue daily. On a ten million yuan project, a month's delay adds roughly 30000-80000 CNY.

On site

Basis

FAQ

Why are calendar days so much longer than working days?
Because sites do not work every day. Rain, high wind that idles cranes, heat, late materials and unapproved preceding work all stop production. The workable-day ratio captures this: 75-85% for general building work, lower in the wet season, and over 90% for interior finishes and services. Hence 27 working days become 32 calendar days. Quoting working days as a duration guarantees overrun.
Does adding people shorten the programme?
Only within limits. Duration follows the critical path, and if a work front only fits ten people, thirty is overcrowding that lowers output. There are practical caps per square metre of front (about 0.5 workers/m² for bricklaying, 0.3 for plastering); beyond that you need zoned or multi-level flow. Real acceleration comes from more fronts, a different method such as precasting, or longer daily hours.
Where do labour norms come from?
From the national or provincial building consumption and pricing norms, which list man-days per unit for each work item. Company history works too: how many cubic metres a gang lays or square metres it plasters in a day gives the real norm. Published values are industry averages, so a well-run crew achieves 1.1-1.3 times them — adjust to your own productivity.

Cite this page

Use this format in reports, method statements or coursework. The link is permanent.

Building Calculator. Construction Duration Calculator. 2026-10-25. https://jianzhujisuan.com/en/construction-duration

Results are estimating aids only and are not a design basis. Construction and final accounts must follow the drawings, the applicable standards and an approved method statement. Anything affecting structural safety, shoring or falsework must be checked by a suitably qualified engineer.