The calculation keeps distance, consumption and price in their stated units

The default scenario counts a 25 km one-way route as a 50 km return journey. At 8.2 L/100 km, it uses 4.1 litres. With an illustrative user-entered price of 195.9 cents per litre, the fuel component is about R8.03 for that return journey. Five such journeys in each of 48 weeks represent 12,000 km. Parking, tolls, servicing, tyres, depreciation, registration and finance are not included.

The cost per 100 km is useful when routes have different lengths: it is consumption multiplied by dollars per litre. Cost per kilometre is that figure divided by 100. These are fuel-only operating measures, not an South African Revenue Service deduction rate and not the full economic cost of owning a vehicle.

Choose a consumption figure that matches the question

New light vehicles display a fuel-consumption label with test results in litres per 100 kilometres. The combined figure is useful for standardised comparison, while urban and extra-urban values provide context. Laboratory test results are not a promise of the number a particular driver will record on a particular road.

Real consumption changes with traffic, speed, gradients, weather, towing, roof racks, payload, tyre pressure, air conditioning, trip length, engine temperature and driving technique. Short cold trips can differ greatly from steady highway travel. A dashboard average may cover a different route mix from the trip being planned.

For a household budget, calculate consumption from several complete fill records where possible. Record odometer distance and litres added, then divide litres by kilometres and multiply by 100. Avoid relying on one partial fill because pump cut-off and vehicle angle can distort the apparent volume. A longer sample is more representative, provided the driving conditions still match the intended use.

Enter a price scenario instead of treating one price as permanent

South African regulated fuel prices can change by product, fuel grade, pricing zone and effective date. This calculator does not fetch a live price, so use a current local forecourt price for a near-term journey and record when it was observed.

For an annual budget, test a central, lower and higher cents-per-litre assumption. If the vehicle uses a particular petrol grade or diesel specification, enter that product’s price instead of a generic headline figure.

The Department of Mineral and Petroleum Resources publishes official fuel-price adjustments. Retail offers, loyalty discounts and station pricing can have conditions, so compare the final price that actually applies to the purchase.

A cheaper station is not automatically a saving if reaching it adds material distance, fuel and time. Compare the expected saving on the planned fill with the added trip cost before making a detour.

Build annual travel from repeated journeys without double-counting

The annual section multiplies the fully counted one-way or return journey by trips per week and weeks per year. If “return trip” is selected, one journey already includes both legs. Enter five journeys for five return commutes, not ten individual legs. If weekday distances differ, calculate each route separately and add the annual totals.

Travel weeks allow for leave, public holidays, working from home or seasonal use. Forty-eight weeks is only an example. A vehicle used for school terms, fly-in fly-out work or irregular client visits needs a pattern that reflects its actual calendar. Optional weekend, holiday and non-work driving should be added as separate route groups rather than concealed in a higher consumption rate.

The comparison vehicle is placed on the same counted distance and price. The displayed saving is therefore caused only by the difference in entered L/100 km. It does not include purchase price, finance, insurance, charging, maintenance, resale value or differences in fuel grade. A vehicle with lower fuel use can still have a higher total cost of ownership.

If the alternative is a battery electric vehicle, do not enter kWh/100 km into the L/100 km field. Electricity has different units and tariffs, and charging losses and public-charging fees require a dedicated calculation. Similarly, plug-in hybrids need a split between electricity and liquid fuel based on charging behaviour and trip length.

Tank range is context, not a refuelling instruction

The optional tank output divides entered usable litres by the vehicle’s consumption and multiplies by 100. It assumes the full entered volume can be consumed at the same average rate. In practice, a fuel gauge, reserve warning, tank specification and filling behaviour do not necessarily identify a safely usable amount with precision.

Do not plan to run a tank dry. Route, weather, road closure, headwind, towing and traffic can reduce range. Remote travel requires appropriate fuel availability checks and a safety plan. The result also says nothing about whether a container, storage practice or transport method is lawful or safe.

Use the trip-litres result to decide whether a planned journey sits comfortably within a known range, then retain a margin. Confirm remote station opening, fuel type and payment arrangements directly. A calculated range based on city consumption may be unsuitable for sand, corrugations, low-range operation or heavy towing.

Use the ledger to test practical changes

After establishing a baseline, change one input at a time. Reducing repeated distance shows the effect of route choice or combined errands. A lower measured consumption can represent tyre maintenance, reduced unnecessary load or smoother driving. A different price shows procurement exposure. Keep the original result so the cause of any saving remains auditable.

Fuel economy should never override road safety. Speed, following distance, fatigue management, load restraint and vehicle condition come first. Follow the vehicle handbook for tyre pressure, fuel grade and maintenance. A mechanical fault, warning light or sudden consumption change warrants appropriate inspection rather than an assumption that driving style explains it.

For business decisions, separate fuel from the full vehicle ledger. Include kilometres, time, tolls, parking, servicing, tyres, registration, insurance, finance and depreciation. For reimbursement or tax, use current employer policy and South African Revenue Service rules rather than this fuel-only estimate. Keep the records required for the method actually claimed.