Two firms assess the same concrete frame. One reports 320 kgCO₂e/m². The other reports 410 kgCO₂e/m². Same building, same spec, different tools — and both claim to be right.
This is the current state of embodied carbon measurement, and it’s creating real commercial problems as clients begin writing carbon targets into contracts. The variance comes from three sources: which life cycle modules are included (A1-A3 only vs. A1-A5), which EPD database is queried (Tally uses US EPDs; One Click LCA uses regional European data), and how conservative the tool is when a specific product EPD isn’t available. One Click LCA, Tally, and Embodied Carbon in Construction Calculator (EC3) each make different assumptions. None is wrong. All are incompatible without a declared methodology.