One of the most common questions from CNG vehicle owners in Bangladesh is: 'How far can I go on a full tank?' Unlike petrol where litres and km have a familiar relationship, CNG involves kilograms, cylinder sizes, and fill levels that confuse many drivers. This guide gives you the formula, typical ranges by car type, and the factors that affect your real-world CNG mileage so you never get stranded.
The Basic Range Formula
CNG Range (km) = Fuel Economy (km/kg) × Usable CNG (kg) Usable CNG (kg) = Cylinder Volume (L) × 0.206 × 0.80 Step-by-step for a 60-litre cylinder: Step 1: Usable CNG = 60 × 0.206 × 0.80 = 9.89 kg Step 2: Range = 9.89 × fuel economy (km/kg) At 18 km/kg: Range = 9.89 × 18 = 178 km At 20 km/kg: Range = 9.89 × 20 = 198 km At 22 km/kg: Range = 9.89 × 22 = 218 km
Typical CNG Range by Car Size
Typical CNG Range in Bangladesh (60-litre Cylinder)
| Car Type | Engine Size | Typical Economy | Range (60L cylinder) | Common Models |
|---|---|---|---|---|
| Microcar / Small hatchback | 0.8L–1.0L | 22–26 km/kg | 218–257 km | Suzuki Alto, Daihatsu Cuore |
| Small sedan | 1.0L–1.3L | 20–23 km/kg | 198–228 km | Suzuki Cultus, Toyota Vitz |
| Mid-size sedan | 1.3L–1.6L | 17–21 km/kg | 168–208 km | Toyota Corolla, Honda Civic |
| Large sedan / SUV | 1.8L–2.0L | 13–16 km/kg | 129–158 km | Toyota Camry, Honda Accord |
| CNG auto-rickshaw | Two-stroke | 30–40 km/kg | 297–396 km | Bajaj, Piaggio |
What Affects Your CNG Mileage?
- Air conditioning: Running AC reduces CNG mileage by 15–25% — a car that does 20 km/kg without AC may drop to 15–17 km/kg with heavy AC use in Dhaka summer.
- Traffic congestion: Stop-and-go Dhaka traffic is 20–30% less efficient than highway driving. Expect lower range when driving in city centre.
- CNG kit quality and calibration: A properly calibrated closed-loop sequential kit extracts 10–15% more km/kg than a poorly tuned venturi kit on the same engine.
- Engine condition: Worn spark plugs, dirty air filters, and low tyre pressure each reduce CNG economy by 3–7%. CNG requires fresh plugs every 20,000 km.
- Driving style: Aggressive acceleration from traffic lights burns disproportionately more CNG. Smooth acceleration and engine braking can improve economy by 10–15%.
- Cylinder fill pressure: If a CNG station fills only to 180 bar instead of 200 bar (common at off-peak times with low line pressure), your actual CNG content is ~10% less than full.
Low Pressure Warning — What to Do
Most CNG vehicles have a pressure gauge on the dashboard showing cylinder pressure in bar. At 200 bar (full), you have maximum range. When the gauge drops below 50 bar, you are in the last 25% of your fuel — equivalent to about 40–50 km in a 60-litre cylinder car. Unlike petrol, CNG pressure drops gradually and then falls off sharply near empty. Do not rely on the gauge reaching exactly zero; the car may cut out before that if station line pressure is also low.
Remaining CNG from gauge reading: Remaining CNG (kg) ≈ (Current Pressure bar ÷ 200 bar) × Cylinder Capacity (kg) Example: 80-litre cylinder at 80 bar Full capacity = 80 × 0.206 × 0.80 = 13.18 kg Remaining = (80 ÷ 200) × 13.18 = 5.27 kg Remaining range (at 18 km/kg) = 5.27 × 18 = 94.9 km
Tip
If you frequently get low-pressure fills at your regular CNG station (gauge not reaching 200 bar after a 'full' fill), try filling at a station on the main pipeline with higher supply pressure — these typically fill to full 200 bar. The difference between a 180-bar and 200-bar fill is about 10% of your tank capacity and ৳40–60 of fuel.