Fuel range calculator
Calculate your boat's maximum range and endurance from tank capacity, burn rate and speed.
Related tools
Worked example
A 200 L diesel tank, 20% reserve, burning 5 L/hr at 6 knots:
- Usable fuel: 200 × (1 − 0.20) = 160 L
- Endurance: 160 ÷ 5 L/hr = 32 hours
- Range: 32 hr × 6 kn = 192 nm
- Absolute max (no reserve): 200 ÷ 5 = 40 hr × 6 kn = 240 nm
Always plan to your reserve range, not your maximum.
How it works
Usable fuel is the tank capacity minus the reserve percentage you want to keep back. Endurance is usable fuel divided by burn rate. Range is endurance multiplied by speed.
Usable fuel = Tank × (1 − reserve%) | Range = (Usable fuel ÷ Burn rate) × Speed
Real range will vary with sea state, wind, fouling and engine load. A 20% reserve is the minimum sensible allowance; 25–30% is safer on longer passages.
Frequently asked questions
Why keep a fuel reserve?
Fuel consumption varies significantly with conditions. A headwind or adverse tide can increase burn rate by 30–50%. Diversions to an alternative port, unexpected repairs or manoeuvring in harbour all eat into your fuel. A 20% reserve is a minimum; on offshore passages many skippers keep 30% or more.
How do I find my engine's fuel burn rate?
Check your engine manual for the consumption curve at various RPM. For passage planning, use your normal cruising RPM (typically 70–80% of maximum). The most accurate method is to measure it yourself: fill the tank, run for a known time at cruising RPM in calm conditions, then check how much you used. Fuel flow meters give real-time data.
Does speed affect fuel range?
Dramatically. Fuel burn on displacement hulls typically scales with the cube of speed. Running at 7 knots instead of 6 knots may increase fuel burn by 40–60% while adding only 17% more speed. Slowing down in a fuel emergency can dramatically extend range. Use this calculator to compare range at different speeds.
How much fuel does a typical boat use?
A 20–25 hp auxiliary diesel in a sailing yacht burns roughly 1.5–3 L/hr at cruising RPM. A 40 hp engine burns 3–5 L/hr. Motor cruisers with larger engines can burn 10–30+ L/hr. Outboard engines vary widely — a 60 hp outboard typically burns 8–15 L/hr at cruise.