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Chartering & Voyage

Ship Fuel Consumption Calculator

This ship fuel consumption calculator estimates daily fuel burn at a new speed from a known reference point, using the propeller (cube) law. It then compares voyage time, bunkers, fuel cost and CO₂ at both speeds, so you can see what slow steaming really saves.

Known consumption

knots
t / day

From noon reports or the speed-consumption table in the charter party.

Planned voyage

knots
nm
USD / t

Example price. Use your latest bunker quote.

3 is the classic cube law; 2.5–3.5 covers most hulls and loading conditions.

Fuel at planned speed

Fuel saved on this voyage

151.6 t

26.5% less fuel · $90,962 · 472 t CO₂

Daily consumption at 12 kn
20.15 t/day
Voyage fuel at planned speed
419.8 t
Voyage fuel cost
$251,895
Days at sea
20.83 days
Extra time at sea
2.98 days

Main engine only. Add auxiliary engine and boiler consumption, which do not fall with speed.

See the effect on your CII rating

Reference vs planned speed

Same ship, draught and weather; propeller law with the exponent above.

At 14 knAt 12 kn
Daily consumption32 t20.15 t
Days at sea17.8620.83
Voyage fuel571.4 t419.8 t
Fuel per 100 nm9.52 t7 t
Fuel cost$342,857$251,895
CO₂ emitted1,779 t1,307 t

How to use the fuel consumption calculator

  1. Enter a speed and daily consumption you trust, for example from recent noon reports in similar weather and loading condition, or from the speed-and-consumption warranty in the charter party.
  2. Enter the planned speed and the voyage distance. The calculator estimates the new daily consumption and compares the whole voyage at both speeds.
  3. Add the fuel type and price to see the bunker cost and the CO₂ emitted, which feed directly into the ship's CII and EU ETS costs.

The propeller (cube) law

The power needed to push a ship through the water rises steeply with speed. As a rule of thumb, main engine fuel per day rises with the cube of speed, so fuel per nautical mile rises with its square:

Daily fuel at V2 = daily fuel at V1 × (V2 ÷ V1)³ Sea days = distance ÷ (V × 24) Voyage fuel = daily fuel × sea days → scales with (V2 ÷ V1)² CO₂ = fuel × Cf (HFO 3.114, LFO 3.151, MGO 3.206 t/t)

The exponent is not exactly 3 for every ship. It tends to be lower for full-form bulk carriers at low speed and higher for fast container ships, and it changes with draught, trim, hull fouling and weather. If you have consumption at two speeds, you can work out your own exponent: n = log(F₂ ÷ F₁) ÷ log(V₂ ÷ V₁).

Worked example: slow steaming from 14 to 12 knots

A ship burns 32 t a day of HFO at 14 knots and has a 6,000 nm voyage ahead.

  • Daily consumption at 12 knots: 32 × (12 ÷ 14)³ = 20.15 t/day
  • At 14 knots: 6,000 ÷ 336 = 17.86 days × 32 t = 571.4 t
  • At 12 knots: 6,000 ÷ 288 = 20.83 days × 20.15 t = 419.8 t
  • Saving: 151.6 t of fuel (26.5%), about USD 91,000 at USD 600/t and 472 t less CO₂, for 2.98 extra days at sea

Whether that is worth it depends on who pays for the extra days. Under a time charter, the charterer pays both hire and fuel, so the break-even depends on the daily hire rate. Under a voyage charter the owner carries the fuel and the time, and laytime, cargo deadlines and market rates all come into it.

Beyond the main engine

  • Auxiliary engines and boilers burn fuel at sea and in port regardless of speed. Add them separately.
  • Running a main engine at very low load for long periods needs the engine maker's guidance on cylinder oil and fouling.
  • Hull and propeller condition can change consumption by 10% or more, so clean hulls make every speed cheaper.

Lower fuel burn improves the ship's CII rating and cuts its EU ETS cost. SENA's ship management team monitors consumption across our fleet every day.

Frequently asked questions

How do I calculate fuel consumption for a voyage?
Divide the distance by speed × 24 to get days at sea, then multiply by the daily consumption at that speed. If you only know consumption at another speed, scale it with the cube law: daily fuel × (new speed ÷ old speed)³.
What is the cube law in shipping?
The rule of thumb that a ship's propulsion power, and so its daily fuel consumption, is roughly proportional to the cube of its speed through the water. It means a small speed reduction gives a large fuel saving.
How much fuel does slow steaming save?
With the cube law, fuel per nautical mile falls with the square of speed. Sailing 10% slower uses about 19% less fuel for the same voyage (27% less per day), although the voyage takes about 11% longer.
Does the cube law work at every speed?
It is a good approximation over a moderate speed range for the same draught and weather. At very low or very high speeds, in heavy weather or with a fouled hull, the real exponent can be well above or below 3, so use measured data where you have it.
How do I convert fuel to CO₂?
Multiply tonnes of fuel by its carbon factor: 3.114 for HFO, 3.151 for LFO, 3.206 for marine gas oil and diesel, and 2.750 for LNG. These are the IMO and EU MRV default factors.
Should auxiliary engine fuel be included?
Yes, for the total bunker requirement and for CII and ETS, but it does not follow the cube law. Estimate it separately from the ship’s typical daily auxiliary and boiler consumption at sea and in port.

Sources & references

Rule-of-thumb estimate for the main engine using the propeller law. Real consumption depends on the ship, draught, trim, hull condition and weather; use measured performance data for commercial decisions.

Last reviewed 8 Nov 2026.

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