Calculator Inputs
Formula used
The calculator compares a project carbon budget to the summed embodied carbon from your material items. If no override is provided, the budget is derived from area and a target intensity.
- Budget (kgCO2e) = Area (m²) × Target intensity (kgCO2e/m²)
- Line total (kgCO2e) = Qty × (A1-A3 EF + A4 EF) × (1 + Waste%/100) × (1 + A5%/100)
- Total (kgCO2e) = Σ Line total
- Achieved intensity (kgCO2e/m²) = Total ÷ Area
- Remaining / Over (kgCO2e) = Budget − Total
How to use this calculator
- Enter gross floor area and a target intensity, or set a budget override.
- Add material items with quantities and emission factors per unit.
- Include transport (A4), waste, and construction allowance (A5) as needed.
- Press Calculate to see totals and remaining allowance.
- Download CSV or PDF to share the assumptions and results.
Example data table
These sample values demonstrate typical inputs only. Replace emission factors with values from your preferred verified sources.
| Material | Qty | Unit | A1-A3 EF | A4 EF | Waste % | A5 % |
|---|---|---|---|---|---|---|
| Concrete (C30/37) | 600 | m3 | 280 | 25 | 3 | 2 |
| Rebar (steel) | 90 | t | 1700 | 50 | 2 | 1.5 |
| Structural steel | 40 | t | 2100 | 60 | 2 | 2 |
| Masonry blocks | 12000 | unit | 1.6 | 0.1 | 5 | 1 |
| Insulation | 3000 | m2 | 2.8 | 0.2 | 8 | 2 |
| Glass | 1200 | m2 | 12.5 | 0.4 | 5 | 2 |
Embodied carbon budgeting in construction
Embodied carbon is the greenhouse gas impact created before a building is occupied. It includes raw material extraction, manufacturing, transport, and on‑site installation. Because these impacts occur early, a clear carbon budget helps teams make better choices while the design is still flexible.
This calculator supports a practical “budget versus spend” workflow. First, define a project budget using either a gross floor area target (kgCO2e/m²) or a fixed contractual allowance (kgCO2e). Next, enter key material quantities and emission factors taken from verified EPDs or your selected database. The tool then totals A1–A3 and A4, and applies allowances for waste and on‑site activities (A5) so your estimate stays realistic for procurement and construction.
Use the results panel to understand where carbon concentrates. A small number of products often dominate the total, such as concrete, reinforcement, and structural steel. When you identify the largest contributors, test alternatives: lower‑cement mixes, optimized structural grids, recycled content, local sourcing, modular components, and tighter waste controls. Re‑run the calculation to see how quickly each change improves your remaining allowance and achieved intensity.
Example workflow using the sample table on this page: assume a gross floor area of 2,500 m² and a target intensity of 450 kgCO2e/m². The implied budget is 1,125,000 kgCO2e. Add the example material lines, then press Calculate. The report shows your total embodied carbon, remaining allowance, and achieved intensity so you can compare options consistently across design stages.
For best outcomes, keep your assumptions transparent. Record the data source for each emission factor, confirm the unit basis matches your quantity take‑off, and update the estimate whenever specifications change. Export the CSV or PDF to share the same inputs with designers, contractors, and clients.
FAQs
1) What does “kgCO2e” mean?
kgCO2e is kilograms of carbon dioxide equivalent. It combines different greenhouse gases into a single comparable impact using standard global warming potentials.
2) Should I use a budget override or an intensity target?
Use an override when a client or policy sets a fixed allowance. Use an intensity target when you want the budget to scale with area and stay comparable across projects.
3) Where do I get emission factors?
Use verified EPDs, national databases, or approved organizational datasets. Ensure the factor covers the correct stage and unit basis (per m³, per kg, per m², or per item).
4) What are A1–A3, A4, and A5?
A1–A3 are product stage impacts. A4 represents transport to site. A5 captures on‑site construction effects and allowances, such as installation losses and site energy, where applicable.
5) How should I set waste and A5 allowances?
Start with your organization’s typical ranges, then refine using contractor feedback and logistics plans. Lower allowances are achievable with tighter procurement, prefabrication, and better storage and handling.
6) Can this replace a full life‑cycle assessment?
No. It is a budgeting and option‑testing tool for early decisions. A full assessment may include additional life‑cycle modules, operational impacts, maintenance, replacement, and end‑of‑life scenarios.
7) How do I keep results comparable over time?
Freeze the methodology: document data sources, scope, and assumptions, then update inputs consistently. Track changes in quantities and specifications so carbon reductions are attributable and auditable.