ASEAN Fuel Economy Calculator
Convert fuel economy between MPG (US), MPG (UK), L/100km, and km/L. Plus compute trip economy from distance + fuel used + fuel price.
Fuel Economy Calculator
🔁 Unit Converter — MPG ↔ L/100km ↔ km/L
📊 Trip Calculator — distance + fuel used → actual economy + cost
US average regular: ~$1.10/L
UK premium: ~£1.45/L
How to use the Fuel Economy Calculator
Convert between fuel economy units
The top section is a pure unit converter. Type any value, pick its unit, and all four standard units are computed: MPG (US) — the US convention; MPG (UK) — the UK/Commonwealth convention (1 UK gallon = 1.20 US gallons, so UK MPG is always higher than US MPG for the same vehicle); L/100km — the metric / European convention (lower is better); km/L — Asian convention (higher is better). A car with "30 MPG (US)" = 36 MPG (UK) = 7.84 L/100km = 12.75 km/L.
Compute your actual trip economy
The "Trip Calculator" section computes your real fuel economy from a logged trip. Drive a known distance, fill up to top off the tank, note the fuel volume. Enter distance + fuel used; the calculator outputs your actual fuel economy in all three standard units. Compare this against your vehicle's EPA / NEDC / WLTP rated number, but expect a gap: the EPA itself says its ratings are useful for comparing vehicles yet may not accurately predict the average you will get, because traffic, hills, AC use, temperature and driving style all move the figure.
Add fuel price for trip cost
Type your local fuel price (per liter or gallon). The calculator outputs total trip cost AND cost per 100km — useful for trip-budgeting, comparing routes, or computing fuel reimbursement. Illustrative reference prices, as at August 2026 (the calculator fetches no prices): Singapore 95-RON ~S$2.85/L (very high), Hong Kong ~HK$28/L, UK premium ~£1.45/L, US regular ~$1.10/L equiv (EIA weekly average, Sep 2026), Malaysia RON95 RM1.99/L for buyers who qualify for the BUDI95 subsidy — everyone else pays the unsubsidised float, about RM4.37/L as at 17-23 September 2026. Mix-and-match — feed Singapore prices into a US miles input or vice versa; the calculator handles unit conversion.
Track over time to spot maintenance issues
Log fuel economy every fill-up over a few months. A sudden drop that your driving and the weather do not explain is worth a check: low tire pressure, a dragging brake, a faulty O₂ sensor or a stuck thermostat can all cost fuel. The EPA notes that a clogged air filter on a modern fuel-injected engine hurts acceleration rather than mileage, so do not expect a new filter to restore the number. For EVs, "fuel economy" becomes kWh/100km — works the same way using the L/100km input as a proxy if you convert kWh to "fuel equivalent" first.
Fuel economy — why your own figure and the rating differ
Every new car comes with an "official" fuel economy number — but the methodology differs dramatically by region. The US uses the EPA-estimated rating (based on city + highway combined cycles tested on a dynamometer). Europe and ASEAN use NEDC (older, very optimistic — being phased out) or WLTP (newer, more realistic). Japan uses the JC08 cycle. All are run on a dynamometer in a laboratory, through standardised driving cycles. The EPA's own guidance is that its ratings are useful for comparing vehicles but may not accurately predict the average you will get, and the same is true of every lab cycle. That's why your dashboard MPG indicator showing "32 MPG" when the sticker said "35 MPG" doesn't mean the car is broken — it means you're driving in the real world.
Why the four units exist and how to read them
The choice between MPG and L/100km isn't just metric vs imperial — they're structurally different scales. MPG (miles per gallon) increases with efficiency — "30 MPG" is better than "20 MPG". But the relationship is non-linear: improving from 20 to 30 MPG saves a lot more fuel than improving from 40 to 50 MPG. This is the "MPG illusion" — a 10 MPG improvement is meaningful only against a baseline. L/100km (liters per 100 km) inverts the metric — lower is better, and the relationship IS linear. Going from 10 to 8 L/100km saves exactly the same fuel per distance as going from 6 to 4. This is why most engineers and government policy work uses L/100km — the math is honest. Asian markets use km/L (kilometers per liter), which is just L/100km inverted — higher is better, non-linear like MPG.
L/100km is the only fuel economy unit where the math is honest. Going from 10 to 8 L/100km saves the same fuel as going from 6 to 4. MPG looks better but distorts the comparison.
What actually affects real-world fuel economy
The figures below are the US EPA's, from fueleconomy.gov. Speed: aerodynamic drag grows with the square of speed, and the EPA notes that gas mileage usually decreases rapidly above about 50 mph (80 km/h). Tire pressure: about 0.2% lost for every 1 psi below the placard figure, so 30% low on a typical 33 psi placard (about 10 psi) costs about 2%. The bigger penalty is tread life, which falls about 1.78% per psi. Cargo weight: an extra 100 lb cuts economy by about 1%, roughly 2% per 100 kg, and it hits small cars harder. Air conditioning: under very hot conditions, more than 25% on a conventional car, particularly on short trips. Aggressive driving (speeding, rapid acceleration and braking): roughly 15% to 30% worse at highway speeds and 10% to 40% in stop-and-go traffic. Cold weather: in city driving about 15% lower at 20°F (−7°C) than at 77°F (25°C), and up to 24% on short trips. The biggest "free" improvement is just driving smoother: anticipating stops, accelerating gently, holding a steady speed on the highway.
The ASEAN fuel-economy + EV transition angle
Fuel economy matters more in ASEAN than most regions because retail fuel prices vary 4×+ across the region. Prices below are illustrative snapshots as at August 2026, not live data; check your local pump price before relying on them. Singapore: highest in ASEAN at ~S$2.85/L for 95-RON petrol (~US$2.05/L) — driven by zero domestic oil + Singapore's policy of pricing fuel close to European levels to discourage car ownership. Hong Kong: similar to Singapore at HK$28/L. Thailand / Philippines / Vietnam: ~$0.90-$1.20/L, mid-range. Malaysia: heavily subsidised, but only for some buyers — under BUDI95, eligible Malaysian citizens pay RON95 at RM1.99/L (~$0.44/L), among the cheapest in the world, while everyone outside the scheme (foreigners, and the vehicle classes it excludes) buys at the unsubsidised managed float, about RM4.37/L as at 17-23 September 2026. The "cheapest in ASEAN" comparison holds for the subsidised tier only. Indonesia: complex tier system — Pertalite RON90 at IDR 10,000/L (~$0.65/L), Pertamax RON92 at IDR 12,500/L. The high-fuel-price markets (SG, HK) are where EV economics have already flipped — at S$2.85/L petrol vs S$0.30-$0.40/kWh charging, a Tesla Model 3 costs ~S$0.05-$0.07 per km vs ~S$0.17/km for a comparable petrol car at 6 L/100km. The EV transition is accelerating fastest in these markets for that reason. In low-fuel-price markets (MY, ID), EV payback is much longer and policy incentives matter more than fuel-cost arithmetic.
Why L/100km is the linear unit, gallons that differ by 20%, and the cost of drag
1 US gallon = 3.785 L. 1 UK / imperial gallon = 4.546 L (20% larger). UK MPG is always higher than US MPG for the same car.
L/100km is the only honest fuel economy unit — its math is linear. Going from 10 to 8 saves the same fuel as going from 6 to 4.
The EPA says its own ratings are useful for comparing vehicles but may not accurately predict the average you will get. Treat any lab rating, EPA, NEDC or WLTP, the same way.
Aerodynamic drag scales with the square of speed, and the EPA notes that gas mileage usually falls rapidly above about 50 mph (80 km/h).
The EPA puts the fuel cost of under-inflated tires at about 0.2% per psi, so 30% low (about 10 psi) costs about 2%. Tread life suffers far more, roughly 18%. Check monthly.
Under very hot conditions the EPA says AC can cut a conventional car's economy by more than 25%, particularly on short trips. Its advice: windows down at lower speeds, AC at highway speeds.
The EPA's combined rating is a weighted average: 55% city, 45% highway. A car's combined figure therefore leans towards its city result.
Aggressive driving (speeding, rapid acceleration and braking) can lower gas mileage by roughly 15% to 30% at highway speeds and 10% to 40% in stop-and-go traffic, according to the EPA.
An EV's "fuel economy" is measured in kWh per distance (kWh/100km, or kWh per 100 miles on a US label). The EPA label also shows MPGe: the miles the car covers on electricity with the same energy content as a gallon of gasoline.
As at August 2026, Singapore charges ~S$2.85/L for 95-RON petrol vs Malaysia's RM1.99/L (~S$0.60) under BUDI95 — driven by Malaysia's heavy fuel subsidies and Singapore's deliberate high-price policy. That gap is the subsidised one: buyers outside BUDI95 pay the unsubsidised float, ~RM4.37/L as at 17-23 September 2026.
Frequently Asked Questions
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Different gallon sizes. 1 US gallon = 3.785 L; 1 UK (imperial) gallon = 4.546 L — the UK gallon is 20% larger. So the same car gets a higher MPG number in UK terms than US terms. A car rated at "30 MPG US" = "36 MPG UK". Always check which gallon a published number refers to. Most modern UK car ads now use L/100km or km/L to avoid the confusion; older British car magazines still use MPG UK.
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The rated numbers come from laboratory tests: standardised driving cycles run on a dynamometer, not on a real road. Real driving has traffic, hills, weather, AC use, cold starts, your specific driving style. The EPA says plainly that its ratings are a useful tool for comparing vehicles but may not accurately predict the average you will get. So a gap on its own is normal. What matters is a change: if your own logged figure falls noticeably without a change in your driving, route or the weather, check tire pressure and brakes.
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L/100km has linear math — going from 10 to 8 L/100km saves exactly the same fuel per distance as going from 6 to 4. MPG is non-linear: improving from 20 to 30 MPG saves a lot more fuel than improving from 40 to 50 MPG (both are "10 MPG improvements" but the first saves 2× the fuel of the second). This is the "MPG illusion" that distorts perception of fuel-economy gains. Government policy, engineering analysis, and fleet-management math worldwide use L/100km for honest comparisons.
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Smoother driving. The EPA estimates that aggressive driving (speeding, rapid acceleration and braking) lowers gas mileage by roughly 15% to 30% at highway speeds and 10% to 40% in stop-and-go traffic, so technique alone is worth more than any accessory: anticipate stops and coast towards red lights, accelerate gently, hold a steady highway speed (cruise control helps), and keep your speed down on long trips, since mileage usually falls rapidly above about 50 mph (80 km/h). Then tire pressure, about 0.2% per psi below the placard (and far more in tread life). Third: removing excess weight, about 1% per extra 100 lb carried. The dashboard "instant MPG" display is a great training tool — drive smoothly to keep it high.
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Use the "fill-up to fill-up" method. (1) At start: fill tank to a clear cut-off (auto-shutoff click), reset the trip meter or note odometer reading. (2) Drive your trip. (3) At end: refill to the same level (auto-shutoff click), note the fuel volume from the pump receipt and the new odometer reading. (4) Enter distance + fuel in the Trip Calculator. The more fill-ups you average over, the more accurate — a single tank can be misleading due to fill-up variation. For best accuracy, log 5-10 fill-ups and average them. Apps like Fuelio, Drivvo, MyMPG do this automatically.
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Heavily depends on local fuel and electricity prices. A worked example with illustrative prices, not live data: Singapore: Tesla Model 3 at ~15 kWh/100km × S$0.35/kWh = S$0.05/km; comparable petrol (Toyota Corolla) at 6 L/100km × S$2.85/L = S$0.17/km. On those numbers the EV costs about 30% as much per km. Run the same arithmetic with your own pump price, electricity tariff and the two cars' consumption: where fuel is subsidised, as in Malaysia and Indonesia, the gap is much narrower, and time-of-use electricity tariffs change the math again.
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It can. The EPA says that under very hot conditions AC use can reduce a conventional car's fuel economy by more than 25%, particularly on short trips, and the effect on hybrids and EVs can be larger in percentage terms. How much depends on the outside temperature, humidity and sun. Open windows cost fuel too, through aerodynamic drag: small at low speeds, larger at highway speeds. The EPA's advice follows from that: roll the windows down at lower speeds and use the AC at highway speeds. Parking in the shade and airing the cabin before switching on the AC also reduce the load.
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Because stop-and-go wastes energy. Every time you accelerate and then brake to a stop, the energy that got the car moving goes into the brakes as heat, and an idling engine burns fuel while covering no distance. Highway driving at a steady speed is mostly fighting aerodynamic drag and rolling resistance, with far fewer of those losses, which is why a conventional car's city rating is normally the lower of the two. Hybrids recover some braking energy into the battery, which narrows the gap.
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No. All calculations run entirely in your browser via JavaScript. There's no server roundtrip — open DevTools → Network and confirm zero outbound requests. Your trip data + fuel prices stay on your device. Safe for fleet-management math, business mileage tracking, or any vehicle data that shouldn't leave your machine.
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Three fuel-economy testing standards. EPA (US Environmental Protection Agency): standardised city and highway cycles on a dynamometer, with the combined figure weighted 55% city and 45% highway; the EPA itself says the ratings are for comparing vehicles and may not predict your own average. NEDC (New European Driving Cycle): the European test from the 1980s, replaced in the EU by WLTP from 1 September 2017. WLTP (Worldwide Harmonised Light Vehicles Test Procedure): the newer procedure, with faster, more dynamic phases meant to bring lab results closer to on-road driving. Japan also used its own JC08 cycle. Figures from different cycles are not directly comparable, so compare cars on the same cycle, or better, on your own logged economy.
Method & sources
How it computes
Unit converter: every input passes through L/100 km — L/100 km = 235.215 ÷ MPG (US), 282.481 ÷ MPG (UK), 100 ÷ km/L — using 1 US gallon = 3.785 412 L, 1 imperial gallon = 4.546 09 L and 1 mile = 1.609 344 km. Trip calculator: distance and fuel are converted to km and litres, economy = litres ÷ km × 100, and cost = litres × price per litre (a per-gallon price is divided by the relevant gallon). Pump prices printed on the page are dated illustrations, not data the tool fetches.
What this tool implements
- NIST SP 811 Appendix B conversion factors: US gallon 3.785 412 L, imperial gallon 4.546 09 L, mile 1.609 344 km; NIST's own rule for mpg → L/100 km, 'divide 235.215 by the number of miles per gallon', is the constant the tool uses.
- MPG (UK) uses the imperial gallon; 282.481 = 100 × 4.546 09 ÷ 1.609 344, and 1 MPG (US) = 1.200 95 MPG (UK).
- Driving-behaviour and maintenance percentages on the page are the US EPA's published figures (fueleconomy.gov); rating cycles (EPA 5-cycle, NEDC, WLTP, JC08) are named for orientation without claimed real-world gaps.
- Reference pump prices are dated snapshots for illustration only; the tool performs no currency conversion and fetches no prices.
Sources
- NIST Special Publication 811, Guide for the Use of the International System of Units (SI), Appendix B.8 — factors for gallon (U.S.), gallon [Canadian and U.K. (Imperial)], mile, and mile per gallon → litre per 100 km. https://www.nist.gov/pml/special-publication-811/nist-guide-si-ap…
- US EPA / US DOE, fueleconomy.gov — Driving More Efficiently (aggressive driving 15–30% at highway speeds and 10–40% in stop-and-go traffic; speed; about 1% per extra 100 lb). https://www.fueleconomy.gov/feg/driveHabits.jsp
- US EPA / US DOE, fueleconomy.gov — Keeping Your Vehicle in Shape (under-inflated tires: about 0.2% per 1 psi below the recommended pressure). https://www.fueleconomy.gov/feg/maintain.jsp
- US EPA / US DOE, fueleconomy.gov — Fuel Economy in Hot Weather (AC can cut a conventional car's economy by more than 25% under very hot conditions) and Fuel Economy in Cold Weather (about 15% lower at 20 °F than at 77 °F in city driving). https://www.fueleconomy.gov/feg/hotweather.shtml
What can make this go out of date
- Pump prices quoted as illustrations (Singapore 95-RON, Malaysia BUDI95 and the unsubsidised RON95 float, Indonesia Pertalite/Pertamax, UK, US) move weekly to monthly and are set by each market's regulator or retailers; the page dates them and nothing refreshes them.
- EPA revises its fueleconomy.gov percentages as it re-runs its studies.
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