In France these measurements have to be made in metres; the product in cubic metres is divided by 0·38 to get tonnage.
Net tonnage, as distinguished from gross tonnage, is the latter less the space occupied by cabins below deck, by engines and bunkers, in short all that is not ‘hold.’
This deduction gives the space available for cargo, a very large proportion in a sailing-ship, a very small proportion in a steam-yacht or tug.
The Cargo Ton is usually reckoned at 40 cubic feet; the space occupied by 20 centals = 4 quarters of wheat, or 25 centals of water.
A steamship of 4500 tons register may be 3000 tons net; as each of these net tons will contain 2-1/2 tons of cargo of about the same weight as wheat, after allowing for cases, dunnage, &c., the ship may be described as carrying 7500 tons dead-weight. Of course, this would only apply to goods of medium weight; not to iron rails or to ore, which could only be taken as a limited part of the cargo, the rest of the space being either filled with light goods or remaining empty.
The ship-owner has the choice of charging freight by measurement, usually at 40 c. ft. to the ton, or by the ton weight for metal and other heavy goods.
Concordance of Capacity, Weight and Measurement
| Capacity | Weight of Water | Cubic Inches | Weight of Wheat Lb. | Cubic Feet | ||||
| Oz. | Lb. | Oz. | ||||||
| 1 | 1·73 | 1/1000 | ||||||
| (1/2 Quartern) | 2-1/2 | |||||||
| 10 | 1/100 | |||||||
| × 8 | = Pint | 20 | = 1-1/4 | 34·6 | 1 | |||
| 100 | 5 | 1/10 | ||||||
| × 8 | = Gallon | 160 | = 10 | 277-1/4 | 8 | |||
| 62-1/2 | 1000 | 50 | 1 | |||||
| × 8 | = Bushel | 80 | 2218 | 64 | ||||
| Cental | 100 | 2 | ||||||
| × 8 | = Quarter | 500 | 10 | |||||
| × 4 | = Ton-cargo | 2000 | 40 | |||||
| = Ton-register | 10 Qrs. | 5000 | 100 | |||||
| With | the | Corn-bushel (U.S.) | = 62-1/2 | lb. | of wheat, | 1 | Quarter | = 500 lb. |
| „ | „ | Imperial bushel | = 64 | lb. | „ | 1 | „ | = 512 lb. |
Table of Volume and Weight of Water