Governing Formula
This is deliberately a screening model, not a database. Each material total is the product of the quantity you enter and the kg CO2e per unit factor you supply; the option total is the straight sum. The engine never guesses factors, scopes, or geographies on your behalf.
kgCO₂e = Σ (m × EF) Where:
-
m= Material quantity in the declared unit (kg, t, m³, m, each…) [varies] -
EF= User-supplied emission factor [kg CO₂e / unit] -
A= Functional (floor) area, optional shared denominator [m²]
Derived Equations:
option = Σ (m × EF) tonnes = kg CO₂e ÷ 1,000 intensity = kg CO₂e ÷ A Δ% = (B − A) ÷ A × 100 How the Calculation Works
Build Option A and Option B, each with one or more material rows. Every row carries a quantity, a unit basis (kg, t, m³, m, each…), and an emission factor in kg CO2e per one unit. The factor’s declared lifecycle scope (e.g. A1–A3, product stage), source reference text, and geography are reproduced with the result so the basis of your comparison stays visible.
The engine sums each option, converts to tonnes (÷ 1,000), and reports Option B relative to Option A as an absolute and percentage difference — making it obvious which design screens lower. If you enter a functional area, both options report the same per-m² intensity for a comparison on one functional unit.
Worked Engineering Example
Design Scenario: 250 t of structural concrete + 30 t of reinforcement
- Option A (baseline) — user factors:
concrete: 250 t × 130 kgCO₂e/t = 32,500 kg•rebar: 30 t × 1,200 kgCO₂e/t = 36,000 kg
total A = 68,500 kg CO₂e (68.5 t) - Option B (low-carbon mix, 28 t rebar) — user factors:
concrete: 250 t × 95 kgCO₂e/t = 23,750 kg•rebar: 28 t × 1,200 kgCO₂e/t = 33,600 kg
total B = 57,350 kg CO₂e (57.35 t) - Comparison: B is lower by
68,500 − 57,350 = 11,150 kg CO₂e—
Δ% = (57,350 − 68,500) / 68,500 × 100 ≈ −16.3% - Intensity at 1,000 m²:
A = 68.5 kg/m²,B = 57.35 kg/m²
Engineering Notes & Design Benchmarks
- Factors must be user-verified. Where possible link them to project-specific Environmental Product Declarations (EPDs), supplier data, or a published national/regional dataset — and record that basis in the Source field.
- Keep scopes consistent. Comparing an
A1–A3(product stage) factor against a cradle-to-grave factor mixes system boundaries and can reverse a true comparison. - Results scale linearly with quantity — this model excludes transport, waste/offcuts, and construction-stage effects unless you bake them into the factor or add them as extra rows.
- Use the tool for relative design screening (A vs B) rather than absolute reporting. Absolute claims usually need a full LCA methodology and verified data.
Assumptions & Limitations
- Every emission factor is user-supplied. The calculator contains no factor database and implies none.
- The engine applies no allocation rules, no unit conversions, and no process modelling: total = Σ(quantity × factor).
- Scope, source, and geography labels are user attributes and are shown for transparency, not as verification.
- The functional area is a user-entered shared denominator; omitting it disables per-m² intensity.
Frequently Asked Questions
What is embodied carbon in construction?
Embodied carbon is the greenhouse-gas impact associated with materials and construction rather than building operation: extraction, manufacturing, transport, construction, and end of life. Product-stage embodied carbon is often labelled A1–A3 (raw material supply, transport, and manufacturing).
Why does the calculator not provide emission factors itself?
Factors vary strongly with geography, grid mix, production route, and product formulation. Hard-coding a factor would silently bias every comparison, so the tool instead asks for your factor and lets you record its scope, source, and geography alongside the result.
What makes a fair A vs B comparison?
The same functional unit (the same quantity and unit basis for comparable materials), the same lifecycle scope (e.g. both A1–A3), and factors that are current for the same geography and date. The calculator can only apply your numbers; it cannot make unequal bases equal.
Can I use this for a formal carbon report?
Not directly. This is a screening and comparison aid. Formal reporting should follow an adopted methodology (for example EN 15978, ISO 14067, or a national framework) with verified data and documented assumptions.
Engineering Disclaimer
Engineering Note: This calculator is a screening model built on user-supplied emission factors. It contains no factor database, performs no lifecycle modelling, and cannot verify the scope, source, or geography of the factors entered. Comparisons are valid only within a consistent functional unit and system boundary; formal reporting requires an adopted methodology and verified data.
Technical References
- ISO 14067: Greenhouse gases — Carbon footprint of products — Requirements and guidelines for quantification and communication.
- EN 15978: Sustainability of construction works — Assessment of environmental performance of buildings (life-cycle stages A–D), CEN.
- EN 15804: Sustainability of construction works — Environmental product declarations — Core rules for the product category, CEN.