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About this tool
Work out the fuel, money and CO2 wasted idling at signals and in traffic, and how much switching off would save.
An idling engine achieves zero kilometres per litre, and this calculator prices that directly. Idle fuel flow is friction plus accessory load rather than anything to do with speed, so it scales with engine displacement — about 0.5 litres per hour per litre of a petrol engine and 0.35 for a diesel, roughly 30% higher again with the AC on. Multiply by the seconds you actually spend stationary with the engine running and you get the litres, rupees and CO2 a year, plus how much of it switching off would recover once each restart's fuel is netted off.
Open Idling Fuel Waste Calculator on AltFTool — it loads instantly in your browser.
Enter the values you already know.
Fine-tune the options to match your scenario.
Read the result and use it in your planning or reporting.
A 2.2 litre diesel and a 1.0 litre petrol do not idle at the same rate, so displacement drives the calculation.
Only idle time beyond the roughly ten seconds a restart costs is counted as recoverable, so the saving is not overstated.
Shows how many kilometres the wasted fuel would have driven, which lands harder than a litre count.
Roughly 0.5 litres an hour per litre of engine displacement for petrol, so about 0.75 L/h for a 1.5 litre engine and 1.0 L/h for a 2.0 litre. Diesels idle leaner at around 0.35 L/h per litre. Running the air conditioning adds about 30% on top, because there is no airflow over the condenser while stationary.
About ten seconds. Restarting a warm fuel-injected engine consumes roughly the fuel of ten seconds of idling, so any halt longer than that is cheaper with the engine off. This is the same threshold factory idle-stop systems use, and why signal-side campaigns target waits of 30 seconds and more.
On a modern car, minimally. Engines designed with idle-stop use reinforced starters and batteries rated for hundreds of thousands of cycles. On an older vehicle, frequent restarts do add wear to the starter motor and battery, so it is worth reserving engine-off for the longer waits rather than every brief halt.
Not on a modern fuel-injected engine — 30 seconds is enough before driving off gently. Extended idling actually warms the engine more slowly than light driving does, wastes fuel, and in a diesel can cause unburnt fuel to wash the bores, so long warm-up idling is a habit worth dropping.
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