⚓ TPC & TPI Calculator

TPC (Tonnes Per Centimeter) is the weight needed to change a ship's mean draft by one centimeter. Use this tool to calculate TPC/TPI, convert units, and predict draft changes.

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TPC from Waterplane Area Inputs

Water Density (t/m³)

Waterplane Area (m²)

Result will appear here

💡When to Use This Tool

When to use TPC from Waterplane Area: Use this marine calculator to determine the Tonnes Per Centimeter (TPC) immersion when the waterplane area is known from the vessel's hydrostatic tables. Essential for precise draft calculations during cargo loading, unloading, or adjusting ballast in different dock water densities.

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Results are for reference only. Please double-check all values.

⚙️ How to Use

Step 1: Choose Mode

Select the calculation mode from the top tabs based on the data you have available.
You can calculate TPC or TPI from area, approximate TPC from dimensions, convert between units, or find draft changes.

Step 2: Enter Data

Input your vessel's metrics (Waterplane Area, Length, Breadth, Cb).
Select the appropriate Water Density if applicable (Fresh 1.000, Sea 1.025).

Step 3: Calculate

Press Calculate to instantly view your results.
The step-by-step methodology is shown below the result for verification.

📘 Formula Reference

TPC from Waterplane Area:

TPC = (Area × Density) / 100

TPC from Dimensions:

TPC ≈ (L × B × Cb × Density) / 100

TPI from Area (Imperial):

TPI = Area (ft²) / 420

Draft Change:

Change (cm) = Weight / TPC

Area = Waterplane Area in m² or ft²

Cb = Block Coefficient

Density = Water density in t/m³

🌍 Common Port Water Densities

Water Type	Density
Fresh Water	1.000 t/m³
Low Brackish	1.005 t/m³
Med. Brackish	1.010 t/m³
High Brackish	1.015–1.020
Sea Water	1.025 t/m³

📖 Terminology & Definitions

TPC (Tonnes Per Centimeter)

TPC is the weight needed to change a ship's mean draft by one centimeter. It is a critical value used in draft surveys and load line calculations.

TPI (Tons Per Inch)

TPI is the imperial equivalent of TPC, representing the weight in long tons required to change a vessel's mean draft by one inch.

Waterplane Area

The horizontal area of a ship's hull intersected by the surface of the water at a given draft.

Block Coefficient (Cb)

The ratio of the underwater volume of a ship to a rectangular block having the same overall length, breadth, and draft.

Relative Density

Standard Sea Water is taken as 1.025 t/m³. Pure Fresh Water is 1.000 t/m³.

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