Work out how much fuel a passage needs and how much carbon dioxide it produces. This marine fuel consumption calculator takes the voyage either as days at sea or as distance and speed, handles the main engine and the auxiliaries on separate grades, and converts the burn to CO₂ using the official IMO carbon factors.
Enter the voyage either as days at sea or as distance and speed. Carbon dioxide is calculated with the IMO carbon factor for each fuel grade.
Main engine
Auxiliaries / boiler
Figures are a planning estimate from the consumption you enter. Actual burn varies with weather, hull and propeller condition, draft and machinery load.
How to calculate ship fuel consumption and emissions
The arithmetic is simple enough to check by hand, which is exactly why the tool shows its working rather than just an answer.
Passage time. If you are working from distance and speed, divide the distance in nautical miles by the speed in knots to get hours, then divide by 24 for days at sea. A 2,400 nautical mile passage at 12 knots is 200 hours, or 8.33 days.
Fuel required. Multiply days at sea by the daily consumption in tonnes. At 22 tonnes a day, that same passage needs about 183 tonnes. The main engine and the auxiliaries are calculated separately because they rarely burn the same grade — a ship on heavy fuel oil at sea is usually running its generators and boiler on marine gas oil.
Carbon dioxide. Multiply the tonnes of each fuel by its carbon factor, written Cf. That factor is the mass of CO₂ released per tonne of fuel burned, and it depends only on the carbon content of the fuel, not on the engine, its condition or its load. Burning 183 tonnes of heavy fuel oil at a Cf of 3.114 produces about 570 tonnes of CO₂.
Sea margin. The optional margin adds a percentage to the calculated burn to allow for weather, currents, hull roughness and propeller condition. Bunker planning normally carries one; a flat calculation from the daily figure does not.
IMO carbon factors used by this calculator
These are the Cf values applied to each grade, the same figures used in EEDI, EEXI and CII reporting. They are listed here so you can check the tool’s assumptions rather than take them on trust.
| Fuel | Cf (t CO₂ / t fuel) |
|---|---|
| Heavy fuel oil (HFO) | 3.114 |
| Light fuel oil (LFO / VLSFO) | 3.151 |
| Marine diesel / gas oil (MDO/MGO) | 3.206 |
| LNG | 2.750 |
| LPG (propane) | 3.000 |
| LPG (butane) | 3.030 |
| Methanol | 1.375 |
What this calculator does not do
It gives you a planning estimate from the consumption figure you enter. It does not predict consumption from the ship’s particulars, and it does not know your hull condition, draft, trim, weather on the route or machinery load — all of which move the real number. Use your own noon report data or the shop trial figures corrected for service condition, not a generic table.
It also does not produce a CII rating. That needs the ship type, deadweight or gross tonnage, the distance covered across the whole reporting year, and the reference line and reduction factor in force for that year. Those are revised annually, so work a rating out against the current IMO resolution rather than any static tool.
Ship fuel consumption calculator FAQs
What is the IMO carbon conversion factor (Cf)?
Cf is the mass of carbon dioxide produced by burning one tonne of a given fuel, and it comes from the fuel's carbon content rather than from the engine. The IMO values used here are 3.114 for heavy fuel oil, 3.151 for light fuel oil, 3.206 for marine diesel and gas oil, 2.750 for LNG, 3.000 and 3.030 for propane and butane, and 1.375 for methanol. They are the same factors used in EEDI, EEXI and CII reporting.
How do I calculate bunker requirements for a voyage?
Divide the distance by the speed to get the passage time in hours, then divide by 24 for days at sea. Multiply those days by the daily consumption to get the tonnes required. A 2,400 nautical mile passage at 12 knots takes 200 hours, or 8.33 days; at 22 tonnes a day that is about 183 tonnes. Add a sea margin on top for weather and hull fouling, and remember to account for auxiliaries and boilers separately if they burn a different grade.
Why do different marine fuels have different emission factors?
Because the factor follows the carbon content of the fuel. LNG is largely methane, which carries four hydrogen atoms per carbon atom, so burning a tonne of it releases less carbon dioxide than a tonne of heavy fuel oil. Methanol is lower again because part of its mass is already oxygen. A lower Cf does not automatically mean lower emissions overall — the energy content per tonne differs too, so a ship may need to burn more tonnes of the lower-carbon fuel to do the same work.
Should I use the LFO factor for VLSFO?
Very low sulphur fuel oil is commonly calculated using the light fuel oil factor of 3.151, but the correct figure depends on the carbon content stated for the specific delivery. If the number is going into a statutory report, take it from the bunker delivery note and confirm it with your verifier rather than relying on a default.
Does this calculate my CII rating?
No. This gives you total fuel and total carbon dioxide for a passage. A CII rating additionally needs the ship type, deadweight or gross tonnage, the distance travelled over the whole reporting year, and the reference line and reduction factor that apply to that year. Those change annually, so a CII rating should be worked out against the current IMO resolution rather than a static tool.
Does the sea margin change the emissions figure?
Yes, because emissions follow the fuel actually burned. The sea margin is an allowance for weather, currents, hull roughness and propeller condition, so it increases both the tonnes required and the carbon dioxide produced. Leave it at zero if you want the flat calculation from your stated daily consumption.