Free marine engineering calculators for work at sea and ashore — sea service for a Certificate of Competency, bunkers and emissions for a passage, and arrival times for a voyage plan. Every tool runs entirely in your browser: nothing is uploaded, nothing is stored on a server, and none of them ask you to sign up.
Certification & sea service
Sea Time Calculator
Add every contract from your discharge book and get the total in days, in whole months at the STCW rate of 30 days to the month, and as the decimal figure application forms ask for. Counts both the sign-on and the sign-off day, merges overlapping contracts so shared days are never counted twice, and shows the gaps ashore separately.
For: Cadets and officers applying for a CoC, an endorsement or a Notice of Eligibility.
Engine room & bunkers
Fuel Consumption & CO₂ Calculator
Enter the voyage as days at sea or as distance and speed, and get the tonnes of fuel required and the carbon dioxide produced. Main engine and auxiliaries are calculated on separate grades, because a ship on heavy fuel at sea is usually running its generators on gas oil. Uses the IMO carbon factors, and prints the whole table so you can check the assumptions.
For: Engineers, superintendents and anyone planning bunkers or reporting emissions.
Everyday reference
Marine Unit Converter
Speed, distance, depth and draft, pressure and temperature, converted as you type. Built around the units actually used at sea rather than a generic converter: cables and fathoms alongside metres and feet, kg/cm² alongside bar for older engine room gauges, and a wind speed to Beaufort force lookup with the sea state and probable wave height.
For: Anyone on watch or in the engine room who needs a figure in different units, fast.
Passage planning
Voyage & ETA Calculator
Work out an arrival time from a planned speed, or turn the question round and get the speed needed to make a laycan or a tidal gate. Everything is computed in UTC and reported in UTC and local time together, with pilot and standby time kept out of the sea passage. Also shows the same voyage at other speeds, so the slow-steaming trade-off is one glance rather than four calculations.
For: Deck officers, agents and charterers planning a passage or checking an ETA.
How these calculators work together
The passage tools are built to hand work to each other rather than sit in isolation. Work out a voyage in the voyage and ETA calculator and the results panel carries a button through to the fuel consumption calculator with the days at sea already filled in. Change the speed, hand it across again, and you can see what slow steaming actually costs in arrival time and saves in bunkers.
The sea time calculator stands on its own, because it answers a different question — not what a voyage costs, but whether your service adds up to the certificate you are applying for.
Who these are for
Cadets and junior officers totalling sea service for an MMD or CoC application. Engineers and superintendents planning bunkers or reporting carbon dioxide. Deck officers, agents and charterers checking whether a laycan is achievable. The tools assume you know your trade — they do arithmetic quickly and show their working, rather than explaining your job back to you.
Why you can check the numbers
Every calculator shows its working rather than producing a figure from nowhere. The fuel calculator prints the full table of IMO carbon factors it applies. The voyage calculator shows the division it performed, in both directions. The sea time calculator states the STCW definition of a month it uses, and flags overlapping contracts instead of quietly absorbing them.
Where a number depends on your administration or your ship rather than on physics, the tools say so instead of guessing. You will not find certificate requirements quoted here, or a CII rating produced from a static table, because those change and a stale figure in an application is worse than no figure at all. The pages link to the authority that publishes the current rules and leave that judgement to you.
These are written and maintained by a practising marine engineer, alongside the engine room articles on this site — the two stroke diesel cycle, uniflow and loop scavenging, the air start system and the crankshaft.
More tools in preparation
Draft survey and trim, under keel clearance and squat, and a merchant navy salary and overtime calculator are in preparation. The order they arrive in depends on how carefully each one needs to be checked before it is safe to publish — a squat figure in particular is not something to get approximately right.