The Pilot’s Book · Trade
How much room goods take
Every good says its room per unit, «m³/unit». Cheap goods are compact, valuable ones bulky: a unit of ambergris takes more than 80 bolts of sailcloth.
Under the name of a good: «0.9 m³/unit» and so on. Valuable goods take more: spices 0.9, medicine 1.1, pearls 1.8, abyssal ore 2.0, kraken ink 2.5, drowned silk 3.0, ambergris 4.2. 
Cheap goods are compact: fish 0.25, salt 0.3, rum 0.55, tobacco 0.65, gunpowder 0.7. Ship's stores are smaller still: 0.05 (planks 0.075). 
The hold's figure in the port window's head shows the room taken and the whole. Count before you buy: half the hold in trade goods is overload (three quarters on a trader).
See also
The hold and overloadTrade goods over half the hold (three quarters on a trader's hull) — overload, −20 % speed. Over the brim — −35 %. Ship's stores do not count.4 steps
The market and pricesEach port has its own prices, and they change every 8 hours. ▲ and ▼ show the trend; luxuries swing the most. Buy cheap here, sell dear there.3 steps
The warehouseA warehouse of 120 m³ in any port: rent is paid once, on the first deposit. «Store all» and «Take all» for each good.3 steps