What lifecycle stages does this cover?

Stages A1 to A3 only — raw material supply, transport to the factory, and manufacturing. This cradle-to-gate boundary is the most common basis for early-design embodied-carbon comparison. It excludes construction (A4-A5), use (B), and end-of-life (C).

Where do the emission factors come from?

From the Inventory of Carbon and Energy (ICE) database version 3.0 by Circular Ecology, a widely used UK reference for embodied carbon of construction materials, expressed in kg CO2e per kilogram of material.

Why does concrete dominate so many buildings?

Concrete has a modest factor per kilogram, around 0.1 to 0.16, but buildings use enormous quantities of it, so it usually makes up the largest single share of structural embodied carbon. Cement production is the main driver; replacing some cement with GGBS or fly ash lowers it.

How does timber compare?

Timber has a low cradle-to-gate factor — often well under 0.5 kg CO2e per kg — and also stores biogenic carbon while it stands, which some assessments credit separately. Substituting timber for steel or concrete in a frame can sharply cut embodied carbon, subject to structural and fire requirements.

How do I compare against RIBA 2030 targets?

RIBA targets are expressed per square metre of floor area (for example under 625 kg CO2e per square metre for offices). Divide your total embodied carbon by the gross internal floor area to get the per-square-metre figure, then compare to the relevant target band.

What is the Embodied Carbon Calculator (Building Materials)?

Add quantities of common building materials by mass to compute embodied carbon in kg CO2e using ICE database v3.0 cradle-to-gate factors (lifecycle stages A1-A3). For architects, structural engineers, and sustainability consultants working toward RIBA 2030 embodied-carbon targets. It runs free in your browser on Gera Tools, with nothing uploaded.

Embodied Carbon Calculator (Building Materials)

Name: Embodied Carbon Calculator (Building Materials)
Creator: Gera Tools
License: https://creativecommons.org/licenses/by/4.0/

Embodied carbon — the emissions locked into a building’s materials before it is even used — now rivals operational energy as a target for the construction sector. This calculator totals the cradle-to-gate embodied carbon of a material schedule using the widely cited ICE database, so design options can be compared quickly at the early stages when design changes are cheapest.

How it works

Each material’s contribution is its mass times its embodied carbon factor, and the building total is the sum:

material CO2e = mass (kg) × ICE factor (kg CO2e per kg)
total = Σ material CO2e over all materials
per m2 = total / gross internal floor area

The factors cover lifecycle stages A1 to A3 (cradle-to-gate): raw material extraction and processing (A1), transport to the manufacturer (A2), and the manufacturing process itself (A3). This boundary is the most common basis for early-design comparison because it is where most of the embodied carbon impact is determined and where design choices have the greatest leverage.

Worked example

A small structural frame uses:

50,000 kg (50 t) of concrete with a factor of approximately 0.13 kg CO2e/kg → about 6,500 kg CO2e
5,000 kg (5 t) of reinforcing steel with a factor of approximately 1.99 kg CO2e/kg → about 9,950 kg CO2e

Total: roughly 16,450 kg CO2e (about 16.5 tonnes). Steel is only a tenth of the mass but contributes 60% of the embodied carbon. This is one of the most important things early-design carbon accounting reveals: the highest-carbon materials by mass-specific factor often dominate the total, so targeting them gives the greatest reduction per kilogram redesigned.

Why the ICE database factors matter

The Inventory of Carbon and Energy (ICE) database, produced by Circular Ecology, compiles embodied carbon factors from published environmental product declarations (EPDs), life cycle assessment (LCA) studies, and industry data. Version 3.0, which the tool references, is a widely accepted source for UK and international early-stage design work.

Factors within the database can have significant ranges depending on production route. For example:

Structural steel produced in an electric arc furnace using recycled scrap typically has a much lower embodied carbon factor than primary steel produced in a blast furnace — the difference can be meaningful.
Concrete embodied carbon varies depending on cement content and whether ground granulated blast furnace slag (GGBS) or fly ash partially replaces Portland cement clinker, which is the most carbon-intensive ingredient.
Engineered timber (CLT, glulam) typically has low cradle-to-gate factors and may sequester biogenic carbon while standing, though the treatment of biogenic carbon varies between assessment methodologies.

Reducing embodied carbon: where the leverage is

Based on the material factors:

Target cement content first — concrete makes up most of a building’s mass; reducing the cement-to-aggregate ratio or substituting cement with GGBS or fly ash cuts the largest single source.
Specify EAF steel — for rebar and structural sections, electric-arc-furnace steel from recycled content has a substantially lower factor than virgin blast-furnace steel.
Consider mass timber where viable — structural timber can replace concrete slabs and steel frames in low-rise and medium-rise applications, often with a significant embodied carbon reduction.
Reduce material quantities — optimised structural design and reduced material waste directly reduce embodied carbon; this is often more impactful than material substitution alone.

Comparing against targets

RIBA, the UK Green Building Council, and other bodies publish embodied carbon targets expressed as kg CO2e per square metre of gross internal floor area. Dividing your total by the floor area gives the figure to benchmark. Note that targets differ by building type and are typically set for the full lifecycle boundary (A1–C4), so an A1–A3 only result will be lower than the full-lifecycle figure for the same building.