What counts as one meal

One swapped meal is two standard serves under the Australian Dietary Guidelines, which treat 65 g of cooked lean red meat and 150 g of cooked legumes as nutritionally equivalent serves of 500–600 kJ. So a meal here is 130 g cooked beef compared against 300 g cooked legumes, such as lentils, chickpeas or split peas. Using the national guidelines rather than a like-for-like weight avoids the common error of comparing portions that deliver very different amounts of protein.

Published data is per kilogram of raw product, so 130 g cooked beef becomes 0.1859 kg raw retail beef (×1.43, a 30% cooking loss) and 300 g cooked legumes becomes 0.120 kg dry. The same masses are used for every one of the four measures.

Savings per meal

The legume emissions factor of 1.25 kg CO₂-e per kilogram breaks down as 0.40 at the farm gate, which is published Australian data, plus 0.35 for cleaning, packing, freight and retail and 0.50 for cooking, both of which are our own allowances.

Where the numbers come from

• Beef: Wiedemann et al. (2015), Journal of Cleaner Production. Australian retail-ready beef, averaged across grass- and grain-finished systems. Cross-checked against Wiedemann et al. (2015) in Animal Production Science. These studies were funded by Meat & Livestock Australia.
• Legume emissions: Simmons et al. (2019), Crop & Pasture Science. Australian grain-legume production at 74 to 672 kg CO₂-e per tonne, cradle to farm gate, by agro-ecological zone. Covers field peas, chickpeas, lentils, lupins and faba beans. Funded by the Grains Research and Development Corporation.
• Legume land: Australian pulse yields from ABARES. Legume water and energy remain our own estimates, held deliberately high. See below.
• Total land: Ridoutt et al. (2013), Journal of Cleaner Production. Six southern Australian beef systems, 86 to 172 m²·yr-e per kg liveweight, weighted for land quality using net primary productivity.
• Car emissions: National Transport Commission. 191 g CO₂/km across all registered Australian light vehicles.
• Household energy: Australian Energy Regulator benchmarks, 15.3 kWh a day.
• Shower volume: 72 L, being eight minutes at nine litres a minute, the maximum flow for a 3-star WELS showerhead.
• Basketball court: 420 m², a full FIBA court of 28 × 15 m.

What we're confident about, and what we're not

Greenhouse gas is the solid number. Independent Australian studies broadly agree on beef emissions intensity, and the gap between beef and legumes is large enough that no reasonable choice of method closes it.

Water and energy are reasonable, with real uncertainty. Australian pulses are mostly rainfed, which keeps their water footprint low, but no Australian legume life-cycle assessment exists at the detail available for beef. Treat these as indicative.

Four things that make these figures conservative. Each central value is the midpoint of the published range rounded down. Beef emissions exclude land use and land-use change, which the same study puts at up to a further 8.7 kg CO₂-e per kilogram. The beef data stops at retail while the legume figures include home cooking, so beef carries less of the supply chain than legumes do. And the car conversion uses the average of all registered vehicles rather than the lower-emitting new-vehicle average. Every one of those choices makes the saving smaller than it might otherwise be.

The greenhouse gas range now varies both sides. Australian data exists for legume production emissions, so that range reflects uncertainty in beef and legumes together. Water, energy and land still vary the beef side only, because no Australian legume figures were available for those, so their true uncertainty is wider than shown.

The two sides are not measured over quite the same span. Beef stops at the supermarket while the legume figures include an allowance for cooking. Correcting that would make our numbers bigger, not smaller: about 2% more on emissions and 22% more on energy. We have not corrected it, because doing so would need figures we cannot source, and because as it stands the inconsistency understates our result.

Legume water and energy are still our own estimates, and we hold them high on purpose. Lowering either would increase the saving we claim, and we would rather understate it until Australian figures are available. The Australian emissions data we did find showed our estimate had been conservative by roughly a third, which is the direction we intend.

Two conversion factors carry no published source. Converting liveweight to retail beef uses a factor of 2.3, and converting household electricity to primary energy uses a factor of 3.0. Both are standard working assumptions rather than cited figures, and the second will drift as the grid decarbonises. The land and energy results move directly with them.

How to read the result

These are modelled estimates for an average meal, not measurements of a specific one. Actual savings depend on the cut of beef, how the cattle were finished, where the legumes were grown and how the food was cooked. Figures are best treated as an order of magnitude, and we publish our ranges rather than a single confident number.