To calculate construction costs accurately, you need to understand the three main resource blocks of a project: materials, labor and equipment. They are the ingredients of every unit price analysis (UPA) and, therefore, of the whole budget.
This guide explains how to calculate each one, with numerical examples you can adapt to your company.
1. How to calculate labor cost
The most common mistake is using the hourly wage that appears on the payslip. The real cost to the company is considerably higher.
Hourly cost formula
Hourly cost = (annual gross salary + employer social security contributions + other costs) / annual productive hours
Other costs may include allowances, per diems, travel, PPE, training or end-of-project severance.
Example
- Annual gross salary of a laborer: €24,000
- Employer social security contributions (≈ 31.5%, indicative rate): €7,560
- Total annual cost: €31,560
- Annual productive hours (per collective agreement, example): 1,736 h
- Hourly cost: €18.18/h
If you add allowances, PPE and travel, the cost can exceed €20/h. Always check the applicable provincial construction collective agreement (Spain).
Labor productivity rate
The productivity rate states how many hours a crew needs to build one unit. For example, for a half-brick (11.5 cm) masonry wall, a crew may need around 0.45 h of skilled bricklayer and 0.225 h of laborer per m².
The best source of productivity rates is your own timesheets: actual hours charged to each line item divided by the quantity completed.
2. How to calculate equipment cost
The hourly cost of an owned machine includes:
- Depreciation: (purchase value − residual value) / useful life in hours.
- Interest and insurance: financing cost of the investment and policies.
- Maintenance and repairs.
- Fuel and lubricants: hourly consumption × price.
- Operator: hourly cost of the machine operator (if not charged under labor).
Example: backhoe loader
- Purchase value: €90,000; residual value (20%): €18,000, so €72,000 to depreciate
- Useful life: 8,000 h
- Depreciation: 72,000 / 8,000 = €9.00/h
- Maintenance and repairs: €4.50/h
- Fuel: 8 l/h × €1.40/l = €11.20/h
- Interest and insurance: €2.30/h
- Operator: €20.00/h
- Total hourly cost: €47.00/h
Rented equipment
For rented machinery, the cost is the rental rate plus transport, fuel (if not included) and operator. Watch out for idle time: a machine standing idle on site still costs money. Keeping a record of equipment rental per project is key to avoiding losses.
3. How to calculate materials
Material quantity
Quantity = measured quantity × consumption per unit × (1 + waste %)
Indicative waste allowances:
- Concrete: 3-5%
- Brick and block: 3-5%
- Mortar: 5-10%
- Tile and flooring: 5-10% (more for diagonal layouts)
- Rebar: 3-5% for offcuts and laps
- Paint: 5-10%
Material price
Always use the delivered-to-site price: supplier price + transport + unloading. If you buy in bulk or have framework agreements, use your actual price, not the price-database figure.
Full example: m² of brick wall
Line item: m² of half-brick wall using perforated brick 24×11.5×9 cm, laid with M-7.5 mortar.
- Skilled bricklayer: 0.45 h × €22.50/h = €10.13
- Laborer: 0.225 h × €18.18/h = €4.09
- Perforated brick: 44 units × €0.15/unit = €6.60 (42 units/m² + 5% waste)
- M-7.5 mortar: 0.026 m³ × €95.00/m³ = €2.47
Calculation:
- Direct cost: €23.29
- Ancillary means (2%): €0.47
- Subtotal: €23.76
- Indirect costs (6%): €1.43
- Unit price: €25.19/m²
If 450 m² are built on the project, the expected cost of the line item will be €11,335.50. With that figure you can later check whether the item stays within budget.
4. Resource explosion: the resource summary
Once all line items are calculated, the estimating software or ERP can generate the resource explosion: the sum of all project resources (skilled labor hours, m³ of concrete, tons of steel…). It is the basis for:
- Planning purchases and negotiating with suppliers.
- Sizing crews and planning the project schedule.
- Requesting bids from subcontractors.
5. From expected cost to actual cost
Calculating well is only half the job. The other half is comparing against what really happens:
- Do the actual hours per m² match the expected productivity rate?
- Does material consumption exceed the estimated waste?
- Is the equipment idle more than planned?
With BIM 2.0 for Odoo, purchases, work reports, staff attendance and equipment rental are charged to each project and line item, so you can see actual versus expected cost in real time. We explain it in how to control project costs.
Frequently asked questions
How much does an hour of a skilled construction worker cost?
It depends on the provincial collective agreement, the job category and allowances. Always calculate the employer cost (salary + social security + other costs) divided by annual productive hours.
How do I calculate actual waste?
Compare the material purchased and consumed on site with the quantity actually built. The difference, as a percentage, is your actual waste.
Should I include the operator in the machine cost?
You can do it either way, but never in both places at once: either in the machine or in labor.
Conclusion
Calculating construction costs rigorously requires employer costs, real productivity rates and delivered-to-site prices. With that data, your budgets will be competitive and your cost control reliable.
👉 Discover how BIM 2.0 connects expected and actual cost: request a demo.