Steamships required a different method of estimating tonnage, because the ratio of length to beam was larger and a significant volume of internal space was used for boilers and machinery.
The Moorsom system calculates the cargo-carrying capacity in cubic feet, another method of volumetric measurement.
King Edward I levied the first tax on the hire of ships in England in 1303 based on tons burthen.
Later, King Edward III levied a tax of 3 shillings on each "tun" of imported wine, roughly equivalent to £150 in 2023.
Since tonnage is calculated by multiplying length × beam × draft × block coefficient, all divided by 35 ft3 per ton of seawater, the resulting formula would be: where: Or by solving : In 1694 a new British law required that tonnage for tax purposes be calculated according to a similar formula: This formula remained in effect until the Builder's Old Measurement rule (above) was put into use in 1720, and then mandated by Act of Parliament in 1773.