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Boat Capacity Calculator
US Coast Guard Formula — Calculate Safe Person, Weight & Engine Capacity
⚓ USCG Formula: For boats under 20 ft without a capacity plate | Persons = (Length × Width) ÷ 15 | Each person = 150 lbs avg
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Max Persons (150 lbs avg)
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Total Weight Capacity
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Available for People + Gear
0 hp
Max Horsepower (est.)
✅ Safety Recommendation
Always operate with at least 10% capacity margin. Check local regulations.
Always operate with at least 10% capacity margin. Check local regulations.
| Item | Weight (lbs) | Notes |
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Calculate safe boat capacity — USCG formula for boats under 20 ft
Boat Capacity Formula — US Coast Guard Method
For boats under 20 feet in length that don't have a capacity plate, the US Coast Guard recommends this formula: Number of persons = (Length × Width) ÷ 15. Each person is calculated at an average of 150 lbs. This calculator goes beyond the basic formula by also estimating maximum horsepower, gear capacity, and providing safety margins.
⚠️ Important Safety Note
This calculator provides estimates based on USCG guidelines. Always check your boat's capacity plate if available. Never exceed manufacturer recommendations. Weather conditions, water type, and operator experience also affect safe capacity.
This calculator provides estimates based on USCG guidelines. Always check your boat's capacity plate if available. Never exceed manufacturer recommendations. Weather conditions, water type, and operator experience also affect safe capacity.
How to Use This Boat Capacity Calculator
- Boat Length & Width: Enter the length and width at the widest point (in feet)
- Boat Type: Select your boat type — affects formula adjustment
- Average Person Weight: Adjust if passengers are larger/smaller than average
- Motor & Gear: Include motor weight and gear to get accurate available capacity
- Results show max persons, total weight capacity, and estimated max horsepower
Understanding Your Results
- Max Persons: Number of adults (150 lb average) boat can safely carry
- Total Weight Capacity: Maximum combined weight of people, gear, and motor
- Available for People + Gear: Remaining capacity after accounting for motor weight
- Max Horsepower (est.): Estimated maximum safe engine power
Boat Type Adjustments
- Monohull: Standard formula (Length × Width ÷ 15)
- Pontoon/Deck Boat: Multiply result by 0.85 (more conservative due to stability)
- Inflatable/RIB: Multiply result by 0.9 (consider load distribution)
Maximum Horsepower Estimation
The USCG also provides a guideline for maximum horsepower: HP = (Length × Width × 1.5) - 25. This is an estimate only. Always check manufacturer specifications and local regulations.
Frequently Asked Questions
- Does this formula apply to all boats? — This is for boats under 20 feet without a capacity plate. Boats with capacity plates must follow those ratings.
- What about children? — The formula uses average adult weight (150 lbs). For children, count them as a fraction of an adult based on weight.
- Does motor weight affect person capacity? — Yes. The total weight capacity includes motor, gear, and people. This calculator subtracts motor weight from available capacity.
- What if my boat has a capacity plate? — Always follow the manufacturer's capacity plate. This calculator is for boats without one.
- How does weather affect capacity? — Reduce capacity by 20-30% in rough weather, high winds, or choppy water.