A stock is the amount of a Product existing at a specified point in time. Unlike flows, which measure the movement or transfer of products over a period of time, stocks are a snapshot measurement of accumulated product quantities at a single moment.
In Life Cycle Assessment and economic modelling, the distinction between stocks and flows is basic. Whilst flows capture dynamic processes such as production rates, consumption rates, or emission rates over time, stocks capture static quantities that exist at a particular moment. For example, the amount of steel in buildings at the end of 2025 is a stock, whereas the amount of steel produced during 2025 is a flow.
Stock accounting plays an important role in understanding material accumulation in the economy and environment. Products can accumulate as stocks in various forms: raw materials in warehouses, goods in retail inventory, products in active use (such as buildings, vehicles, or infrastructure), and materials in landfills or other disposal sites. Changes in stock levels over time result from the difference between inflows (such as production or imports) and outflows (such as consumption, exports, or disposal).
The concept of stocks extends beyond physical products to include stocks of natural resources (such as fossil fuel reserves or forest biomass), stocks of emissions in environmental compartments (such as carbon dioxide in the atmosphere), and stocks of economic value (such as capital goods).
As Chief Operating Officer, Iris leads our organisational development and oversees day-to-day operations. Before joining 2-0, she worked in the biotechnology sector. As an LCA consultant, Iris has devoted her expertise primarily to the domains of sustainable agriculture and food production. She is dedicated to teaching LCA and is responsible for our educational efforts. Iris holds an M.Sc. in Biology – Biotechnology from the University of Copenhagen.
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Glossary terms are clearer once you have seen them applied. Our guide to what LCA is and how it works walks through the complete methodology: goal and scope, inventory modelling, impact assessment, and interpretation.
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