Convert g CO₂e/tonne-km to g CO₂e/tonne-nautical-mile
Sea freight is the low-carbon workhorse of global trade, and its intensity is measured per tonne-nautical-mile — one tonne of cargo carried one nautical mile — because ships navigate in nautical miles. Logistics standards use the tonne-kilometre, so the two need reconciling. A nautical mile is longer than a kilometre (1.852 km), so a per-tonne-nautical-mile figure is larger: per tonne-nautical-mile = per tonne-km × 1.852. It works the same for CO₂ and CO₂e.
To convert g CO₂e/tonne-km to g CO₂e/tonne-nautical-mile, multiply by 1.852 (1 nautical mile = 1.852 km). So container shipping at 12 g CO₂e/tonne-km is 12 × 1.852 ≈ 22 g CO₂e/tonne-nautical-mile. To reverse it, multiply by 0.539957.
g CO₂e/tonne-nmi = g CO₂e/tonne-km × 1.852. Reverse: g CO₂e/tonne-km = g CO₂e/tonne-nmi × 0.539957. The 1.852 is a nautical mile in kilometres — exact, by international definition (one minute of latitude). The intensity is larger per nautical mile because the tonne travels a longer unit of distance.
| Intensity | × 1.852 | Per tonne-nautical-mile |
|---|---|---|
| 4 g/tonne-km (bulk carrier) | × 1.852 | 7.4 g/tonne-nmi |
| 12 g/tonne-km (container) | × 1.852 | 22.2 g/tonne-nmi |
| 7 g/tonne-km (tanker) | × 1.852 | 13.0 g/tonne-nmi |
| 1 g/tonne-km | × 1.852 | 1.852 g/tonne-nmi |
Nautical mile, statute mile, kilometre
Three distance units turn up in freight, and they are all different. The nautical mile (1.852 km) is used at sea; the statute mile (1.609 km) on land; the kilometre in international logistics standards. So a tonne-nautical-mile is about 15% longer than a tonne-(statute)-mile, and 85% longer than a tonne-km:
| Distance unit | Kilometres | Used for |
|---|---|---|
| Kilometre (km) | 1 | GLEC, ISO 14083 (all modes) |
| Statute mile | 1.609344 | US road & rail freight |
| Nautical mile (nmi) | 1.852 | Shipping & aviation |
Don’t use the road/rail tonne-mile converter (×1.609) for sea freight — a nautical mile is 1.852 km, about 15% longer, so it needs ×1.852. Also, the IMO’s Carbon Intensity Indicator is measured per capacity-nautical-mile (deadweight or gross tonnage × distance), not per tonne of actual cargo — a different denominator that this converter does not touch.
Sea-freight intensities, both ways
Indicative carbon intensities for ship types, in both units. Sea freight is the lowest-intensity mode by far — a fraction of road, and orders of magnitude below air — because a large ship moves an enormous mass very efficiently:
| Ship type (indicative) | g CO₂e/tonne-km | g CO₂e/tonne-nmi |
|---|---|---|
| Bulk carrier (large) | ~4 | ~7 |
| Oil tanker | ~7 | ~13 |
| Container ship | ~12 | ~22 |
| General cargo | ~15 | ~28 |
Indicative order-of-magnitude figures; real intensities vary with ship size, load factor, speed and route. For comparison, road freight is roughly 80 g/tonne-km and air freight around 600 — which is why moving cargo by sea rather than air is one of the largest levers in logistics decarbonisation.
g CO₂e/tonne-km to g CO₂e/tonne-nautical-mile conversion table
The table reads both ways — per tonne-km to per tonne-nautical-mile on the left (× 1.852), back again on the right (× 0.539957).
| g/tonne-km | → per tonne-nmi (× 1.852) | g/tonne-nmi | → per tonne-km (× 0.539957) |
|---|---|---|---|
| 1 | 1.85 | 1 | 0.540 |
| 4 | 7.41 | 10 | 5.40 |
| 12 | 22.2 | 25 | 13.5 |
| 50 | 92.6 | 100 | 54.0 |
| 100 | 185.2 | 250 | 135.0 |
Where these units are used
- Shipping and maritime data. Ship distances and the IMO’s Carbon Intensity Indicator use nautical miles, so a shipping figure is naturally per tonne-nautical-mile (or per capacity-nautical-mile).
- Logistics carbon accounting. The GLEC Framework and ISO 14083 express all modes per tonne-km, so a per-tonne-nautical-mile sea figure must be converted to sit alongside road, rail and air in the same chain.
- Estimating sea-freight emissions. The intensity multiplies tonne-nautical-miles of shipping; the sea freight calculator does the full Scope 3 estimate, while this converter aligns the distance unit.
- Molecule-agnostic. As a per-tonne-per-distance intensity, the factor is identical for CO₂, CO₂e or any single gas — CO₂e just bundles all gases into a CO₂-equivalent first.
Frequently Asked Questions
Multiply the per-tonne-km figure by 1.852 (a nautical mile is 1.852 km). For example, container shipping at 12 g CO₂e/tonne-km is about 22 g CO₂e/tonne-nautical-mile. To reverse it, multiply by 0.539957. The factor is exact and applies to CO₂ and CO₂e alike.
A nautical mile was defined as one minute of latitude along a meridian, and is now fixed by international agreement at exactly 1,852 metres. It is longer than a statute mile (1.609 km), which is why sea-freight distances and intensities differ from road figures.
No — a nautical mile is about 15% longer than a statute mile, so a tonne-nautical-mile carries 15% more distance than a tonne-mile. Use ×1.852 for sea freight (nautical miles) and ×1.609344 for road and rail (statute miles); don’t mix them up.
Not exactly. The IMO Carbon Intensity Indicator is per capacity-nautical-mile — deadweight or gross tonnage times distance — not per tonne of actual cargo. It measures a ship’s efficiency by its capacity, so it isn’t directly comparable to a cargo-based tonne-nautical-mile figure without knowing the load.
A large ship moves an enormous mass of cargo with relatively little energy per tonne, so its carbon intensity — a few grams per tonne-km — is a fraction of road freight (~80 g) and orders of magnitude below air (~600 g). Shifting cargo from air to sea is one of the biggest levers in cutting freight emissions.
No. Converting a per-tonne-per-distance intensity between units doesn’t depend on which gas it is, so the factor is identical for CO₂, CO₂e or any single gas. CO₂e just means the gases have already been combined into a CO₂-equivalent using their global warming potentials.