Ballast Ratio Calculator
Ballast ratio is one of the simplest sailboat design numbers: the proportion of total weight that is ballast. It hints at how much sail a boat can carry before heeling too far. Enter the ballast weight and the total displacement in the same units to get the ratio as a percentage. Remember that ballast ratio ignores keel depth and hull form, so treat it as a quick comparison rather than a full stability assessment.
Ballast ratio formula
Ballast ratio (percent) = ballast weight / displacement * 100
Ballast ratio (fraction) = ballast weight / displacement
Use the same unit for both weights. The ratio is dimensionless, so pounds or kilograms give the same answer.
Worked example
- Ballast 4,000 lb, displacement 12,000 lb.
- Ballast ratio = 4,000 / 12,000 * 100 = 33.33 percent.
- That is a typical cruiser figure.
Ballast ratio: frequently asked questions
What is ballast ratio?
Ballast ratio is the weight of a sailboat's ballast (usually the keel) divided by its total displacement, expressed as a percentage. Ballast ratio = ballast weight / displacement * 100. It is a rough index of stiffness: a higher ratio generally means the boat can carry more sail before heeling excessively.
What is a typical ballast ratio?
Many cruising sailboats fall in the range of about 30 to 40 percent, and performance designs can exceed 40 percent. Values below about 30 percent are common on light or beamy boats that gain stability from hull form rather than ballast. These are general guides, not strict limits.
Does a higher ballast ratio always mean more stable?
Not on its own. Ballast ratio ignores how low the ballast sits and the hull's form stability. A boat with a lower ballast ratio but a deeper, bulbed keel can be stiffer than one with more ballast carried higher. Ballast ratio is a quick comparison, not a complete stability measure.
What weights should I enter?
Enter the ballast weight (the keel or internal ballast) and the total displacement in the same units, pounds or kilograms. The ratio is dimensionless, so as long as both use the same unit the percentage is correct.
Official sources
- U.S. Coast Guard: recreational boating safety and stability.
- NIST: unit conversions (pound, kilogram).
Reviewed by the CalculatorHub team, edited by James Graham, 19 June 2026. See our methodology.