Method: gas requirement is calculated from the volume of water to bring to the boil (people × boils × days), weighted by stove efficiency, temperature, wind and altitude, plus a 10% margin. For each brand, the canister combination is the one that covers the requirement with the fewest canisters possible — except for trips of 3 days or more, where the 450 g canister is set aside in favour of the 230 g as long as it remains reasonable (max 5 canisters), to limit bulk and allow progressive load-shedding.

What's the difference between canisters? Primus, MSR, Jetboil and Optimus all use the standard screw valve (EN417): a canister from one brand screws onto a stove from another without any issue. What really differs is the gas blend: standard canisters (Power, IsoPro, JetPower, Energy) are a butane/propane mix designed for temperate conditions, while the "Winter" versions (Primus) or "4 Seasons" versions (Optimus) contain more propane for better vaporisation in extreme cold. One more point: for Primus, the 450 g size is not available in our catalogue — beyond 230 g, you simply use multiple 230 g canisters, which ties in with the "compact format" logic above.

Sources and limitations: benchmarks based on REI Co-op and MSR (Cascade Designs) recommendations for trek planning. An estimate, not a guarantee: actual performance depends on your equipment, technique, and factors not modelled here (melting snow, canister wear, etc.). In extreme cold or demanding terrain, always carry a spare canister.