CalcFuel calculation logic lives in a shared domain layer so tools stay consistent. This page summarises the main methods. Individual calculators also include an on-page methodology note.
Fuel used
- Imperial: gallons = distance (miles) ÷ MPG.
- Metric: litres = (L/100km ÷ 100) × distance (km).
Fuel cost = fuel volume × price per unit.
MPG ↔ L/100km
We use the standard conversion factor ≈ 235.215 (based on US gallons and kilometres). km/L = 100 ÷ L/100km.
Marine trips
Primary path: burn rate × travel time (distance ÷ speed). Safe range uses usable tank capacity after a reserve fraction (default 15%). HP-derived burn is an optional rule of thumb only.
Towing
A percentage penalty worsens efficiency (higher L/100km or lower MPG). Extra cost is towing fuel cost minus unloaded fuel cost for the same distance.
Vehicle running cost
Hybrid comparisons take the annual fuel saving plus any maintenance advantage and divide the purchase premium by it to give a break-even in years. EV comparisons add electricity (mi/kWh or kWh/100km), maintenance and insurance over a chosen horizon.
Two things these models deliberately exclude. Depreciation is left out because it depends on make, variant, condition and market timing far more than on drivetrain, and including a guess would swamp the fuel arithmetic the tool exists to do. Finance cost is left out for the same reason — a purchase premium paid in cash and one carried on a loan are different problems.
Generator consumption
Hourly burn = rated output (kW) × applied load (%) × a fuel-specific consumption rate in litres per kilowatt-hour: approximately 0.30 for diesel, 0.42 for petrol and 0.55 for liquid propane. Imperial output converts at 3.78541 litres per US gallon.
These rates describe a generator working at a reasonable load. Small sets running at very light load are materially less efficient per kilowatt-hour than this model assumes, so size fuel storage above what it reports rather than to it.
Fuel prices
Prices last updated (9 days ago) — ACCC thirtieth weekly report, published Friday 2 October 2026. Per-city figures and methodology.
Default prices are the five-city daily average from a single named, dated ACCC weekly fuel price monitoring report, transcribed without modification. The full dataset, the report it came from and the update procedure are published on Australian fuel price data. In the repo, the figures live in src/lib/fuel-prices.ts and the refresh steps are in docs/accc-price-refresh.md. A build-time cadence check fails when that snapshot’s pricesTo date is 14 days old or older (configurable via ACCC_STALE_AFTER_DAYS; 7 is the tighter same-week option). Prices are always overridable — a local pump price beats any city average.
Separately, when to buy petrol transcribes ACCC buying tips for the five largest cities three times a week and maps the tip language to a cycle phase. Those phases are a CalcFuel label for ACCC wording, not a cents or cheap-day forecast. The data lives in src/lib/accc-cycle-tips.ts; the refresh steps and tip-to-phase table are in docs/accc-cycle-tips-refresh.md. A build check fails when the oldest tip is 7 days old or older (override with CYCLE_TIPS_ALLOW_STALE=1). Diesel has no phase — ACCC states it does not cycle.
Ages such as “6 days ago” are whole calendar days in Australia/Sydney, computed when the page is rendered and again in the browser, so a cached copy does not keep yesterday’s count. Pages that show that age or a stale flag revalidate hourly. When the oldest buying tip is 7 days old or older at that render, the city phase labels are hidden and the page says the tips are paused. The diesel section and the ACCC link stay.
Worked examples
Every calculator carries a worked example with the arithmetic shown step by step. Each one is produced by running that scenario through the calculator itself, so if a formula changes and an example is not updated with it, the two disagree visibly on the page rather than silently in the code.
Limitations
Every model here is a simplification, and each calculator states the specific simplification it makes. The common ones: manufacturer economy ratings run roughly 10–20% optimistic against real-world use; aerodynamic effects — which dominate towing and marine consumption — scale with speed far faster than intuition suggests; and short trips from cold consume well above a vehicle’s rated figure for the first few kilometres.
None of these tools produce a guarantee, and none should be the only input to a decision with real money or real safety margin attached. For anything on the water, plan to the reserve rather than to the range. See also our editorial policy and corrections process.