An idling engine burns fuel while going nowhere. A typical 2-litre petrol car uses about 1.2 L (0.3 gallons) an hour, and larger engines more. Turning the engine off for stops longer than about 10 seconds saves fuel in a warm modern car – which is why many cars now have stop-start systems.
How to use the Idling Fuel Consumption Calculator
- Fuel
- Engine size
- Idling per day
- Days
- Fuel price
Results update as you type, and every field accepts the units shown in its menu.
How it works
Choose petrol or diesel, enter the engine size, the minutes you idle per day and for how many days, and the fuel price.
Tips
- Use your own measured figures – fuel economy, speed and prices vary a lot with driving style, traffic, load and season.
- Pick the unit in each field’s menu (miles or kilometres, mpg or L/100 km); the calculator converts everything for you.
- Fill up to the brim twice and divide the distance by the fuel added to measure real fuel economy.
- For vehicle modifications, treat results as a starting point and confirm with the parts maker or a professional mechanic.
Common mistakes to avoid
- Mixing US and imperial (UK) gallons – a UK gallon is about 20% bigger.
- Using the advertised fuel economy instead of real-world figures.
- Forgetting tolls, parking and wear and tear when comparing driving with public transport.
Inputs explained
| Field | What to enter |
|---|---|
| Fuel | Choose one: Petrol, Diesel |
| Engine size | Units: L, cc, in³ |
| Idling per day | In min |
| Days | A number |
| Fuel price | Units: /US gal, /L, /UK gal |
What each result means
- Idle fuel consumption = [Engine size]×[Fuel]×0.001÷3600
- Fuel used = [Idle fuel consumption]×[Idling per day]×60×[Days]
- Cost of idling = [Fuel used]×[Fuel price]
Example values
How the main result changes when Engine size changes and everything else stays at the example values above:
| Engine size (L) | Fuel used (US gal) |
|---|---|
| 1 | 9.9 |
| 1.5 | 14.9 |
| 2 | 19.8 |
| 2.5 | 24.8 |
| 3 | 29.7 |
| 4 | 39.6 |
Formula
Idle consumption (L/h) ≈ engine size (L) × 0.6 (petrol) or × 0.45 (diesel)Fuel used = idle rate × idle time; cost = fuel × priceWorked example
Inputs — Fuel: Petrol; Engine size: 2 L; Idling per day: 15 min; Days: 250; Fuel price: $3.5 /US gal.
Results — Idle fuel consumption = 1.2 L/h; Fuel used = 19.8 US gal; Cost of idling = $69.35; CO₂ emitted = 173 kg.
Frequently asked questions
How much fuel does idling use?
About 0.5–0.7 L per hour per litre of engine size for petrol engines – roughly 1–1.5 L/h for a typical car.
Is it better to idle or restart?
For a warm engine, restarting uses less fuel than idling for more than about 10 seconds.
Does idling warm up the engine faster?
No – gentle driving warms it faster and with less wear than idling.
What formula does the Idling Fuel Consumption Calculator use?
Idle consumption (L/h) ≈ engine size (L) × 0.6 (petrol) or × 0.45 (diesel).