About this calculator
When planning cargo for a ship you do not know yet, or comparing several candidate charter vessels, often only the main dimensions are available: LBP (length between perpendiculars), beam, depth and draft. This calculator turns those into capacity estimates with basic naval architecture formulas.
Underwater volume = L × B × T × Cb (the block coefficient: how "full" the hull is compared with a box). Multiplied by the water density (1.025 t/m³ for sea water) this gives the displacement. Less the empty ship weight (lightship) it becomes the deadweight (DWT) — all cargo, fuel, fresh water and stores the ship can carry. The waterplane coefficient is estimated with Cw ≈ (2·Cb + 1) ÷ 3, then TPC = L × B × Cw × ρ ÷ 100 (tonnes per centimetre immersion).
For cargo space, the hold length is taken as a share of the LBP, reduced by the double bottom height and side tank width, then multiplied by a hold fullness factor. TEU capacity counts 20' bays (pitch about 6.5 m), rows (about 2.55 m) and tiers (about 2.59 m) in the holds and on deck, corrected for the tapering ends of the hull. The result is an order-of-magnitude estimate for early planning; the official figures are in the ship's capacity plan, hydrostatic tables and load line certificate.
Worked example
Ship LBP 120 m × beam 20 m × depth 10 m, draft 7.5 m, Cb 0.70, lightship 3,900 t:
- Volume = 120 × 20 × 7.5 × 0.70 = 12,600 m³ → displacement × 1.025 = 12,915 t; DWT 9,015 t
- Cw = (2 × 0.70 + 1) ÷ 3 = 0.80 → waterplane 1,920 m² → TPC 19.68 t/cm
- Holds 70% × 120 = 84 m × 20 × (10 − 1.5) × 0.85 = 12,138 m³
- TEU: 12 bays × (6 rows × 3 tiers in hold + 7 rows × 3 tiers on deck = 39) = 468 slots × 0.85 = about 398 TEU
How to use it
Enter main dimensions
Enter LBP, beam, depth and loaded draft in metres, plus the water density.
Choose the block coefficient
Pick a ship type preset (container about 0.65, general cargo 0.72, bulk 0.83, barge 0.92) or enter your own Cb.
Enter lightship
Enter the empty ship weight from the specification; without it DWT cannot be estimated properly.
Adjust cargo space assumptions
Adjust hold length share, double bottom, side tanks and deck tiers for the m³ and TEU estimate.