Construction calculators
17 construction calculators: duration and line-of-balance programme, labour days, plaster and mortar, laydown area, wellpoint dewatering, bored piles, soil nails, striking time, waterproofing, gutters and asphalt.
⬡High Strength Bolt Torque CalculatorPreload by size and class, with snug and final torque.▤Plaster and Render CalculatorMortar, cement and sand by layer for internal plastering.◐Mortar Mix Design CalculatorTrial strength, cement, water and sand, and the mix by mass.⚒Labour Days and Crew CalculatorMan-days, crew size and labour cost from output rates.⇉Line-of-Balance Duration CalculatorRhythmic flow duration with overlap and break adjustments.▥Material Storage Area CalculatorNet footprint, total area and a suggested bay size.◍Dewatering CalculatorPit inflow by the equivalent-well method, then well count.⊙Bored Pile Concrete and Rebar CalculatorConcrete volume, overbreak factor and reinforcement for bored piles.◷Formwork Striking Time EstimatorStriking times for side and soffit forms by member and temperature.▧Waterproofing Area and Membrane CalculatorTotal area with upstands, membrane rolls and primer.⊵Wellpoint Dewatering CalculatorPoints along the pit perimeter: count, spacing, header length and daily pumping.⊿Soil Nail Wall CalculatorNail count and length, grout volume, facing concrete and mesh.◷Construction Duration CalculatorQuantity × labour norm ÷ crew gives the days you need.◫Bathroom Waterproofing CalculatorFloor, walls and detail strips, with coating and membrane quantities.⌄Roof Gutter CalculatorDesign flow, what the gutter can carry, and how many downpipes.≣Waterstop CalculatorJoint length gives waterstop length, area and weight.▩Asphalt Quantity CalculatorArea × thickness × density gives tonnage, then bitumen content.
What this group solves
This group is for planning: durations, flow, crew sizes, laydown space and dewatering choice. Duration comes from the number of sections, the cycle time per section and any lag, while labour days come from quantity divided by output norm — and the two must agree, because a programme that does not match its crew is the most common reason a method statement comes back.
The other half is specialist processes: dewatering sized from total inflow and yield per well, bored piles from diameter and depth, soil nails from face area and grout take, waterproofing from area plus laps and detail reinforcement, waterstops from joint length plus laps, and asphalt where bitumen ratio is not the same as bitumen content. Every one of these has an add-on that gets forgotten, and each is broken out separately here.
This group does not produce a single number, it produces a plan: duration sets how many crews you need, crew count sets the labour peak, and the peak sets site storage and temporary facilities. So sequence duration first, then the flow, then people and space. Working backwards from a headcount to a duration usually means the programme is already behind at the first floor.
Which one for your case
| Overall or per-block construction duration | Construction Duration Calculator |
| Flow-line scheduling — takt and step | Line-of-Balance Duration Calculator |
| Crew size back-calculated from quantities | Labour Days and Crew Calculator |
| How much laydown area the site needs | Material Storage Area Calculator |
| When formwork can be struck | Formwork Striking Time Estimator |
| Concrete volume for bored piles | Bored Pile Concrete and Rebar Calculator |
| Tightening torque for high-strength bolts | High Strength Bolt Torque Calculator |
| Waterproofing turn-up height in bathrooms | Bathroom Waterproofing Calculator |
| Waterstop plate length | Waterstop Calculator |
Where this group goes wrong
- Estimating duration as floor area ÷ output per man, ignoring structural form and season. Two 10,000 m² jobs differ by two months between frame and shear wall, and winter working in the north adds one to two months more; in the south, earthworks and basements need 15-20 rain days.
- Dividing scheduled man-days by the duration. Those are whole-job averages; site headcount has to be set on the peak, which runs 1.3-1.5 times the average. Staff to the average and the programme falls behind before topping out.
- Bored pile concrete without an overbreak factor. Design diameter gives a nominal volume; actual placement needs 1.05-1.2, and 1.3 in gravel or below the water table. On 100 piles of Φ800 × 20 m, missing 1.15 is 180 m³.
- Striking formwork on a blanket seven days. Soffit formwork follows matching-cured cube strength: 100% above 8 m span, which for C30 in winter can mean 21 days. Striking early is not a cracking problem, it is a collapse problem.
FAQ
How do I estimate a construction duration?
Quantity divided by the output norm gives labour days, then divide by crew size for duration in days, then arrange the sections as a flow. With n sections, m trades and cycle time t, a balanced flow takes (n + m − 1) × t plus technical breaks less any overlap. Only the critical path can compress the total.
How many wellpoints do I need?
Total pit inflow divided by yield per well — typically 1.5-2.5 m³/h — gives the count. Spacing runs 0.8-1.6 m, and a single-stage system draws down 3-6 m; beyond that you need two or more stages. Riser length is drawdown plus filter length plus 0.5 m above ground.
How many rolls of waterproofing membrane?
Area divided by roll coverage (commonly 10 m²), times one plus lap waste. With 100 mm side laps and 150 mm end laps that is 10-15%. Add detail strips 300-500 mm wide at corners, penetrations and construction joints — usually another 5-8%, and the part most often left out of the order.
How should construction duration be estimated?
In two stages. Structure at 5-7 days per floor (4 with shear walls and aluminium formwork), fit-out at 15-25 days per floor. Basements are counted separately and usually take 25-35% of the total — two basement levels often cost as much time as ten floors above ground. Then add rain days and winter stoppage for the season.
How is the final tightening torque for high-strength bolts set?
T = K × P × d, with K around 0.13 (0.11-0.13 for tension-control bolts), P the installation pretension and d the nominal diameter. For M20 grade 10.9, P = 155 kN, giving about 0.13 × 155 × 20 ≈ 403 N·m. Adjust to the torque coefficient from the incoming test — do not copy the figure.
How high must bathroom waterproofing turn up?
1.8 m on shower walls, 0.3 m elsewhere, 0.75 m around a bath, and 0.5 m beyond the door opening, with the floor fully covered. Measure from finished floor level, not structural level — inspections fail on this regularly because the screed eats several tens of millimetres of the height.
How is formwork lateral pressure calculated?
Per GB 50666, take the lesser of the fresh-concrete pressure formula value and concrete unit weight × pour height. High slump, retarders and low placement temperature all raise it, so column forms and tie rods for highly workable mixes must be designed from the calculated value rather than habit.
Other groups
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.