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Boat Winterization Calculator

Calculate antifreeze and shrink wrap for winter storage

Units

Total Antifreeze Needed

15.8

gallons (buy 16)

Antifreeze Cost

$192

Total w/ Wrap

$542

Shrink Wrap

Material Needed

794 sq ft

Rolls / Cost

1 / $350

Antifreeze by System (gallons)

Engine(s)3 gal
Water System10 gal
Holding Tank2.8 gal

Winterization Checklist by System

SystemAntifreeze (gal)Key Steps
Engine1.5–5.0Flush, drain, run antifreeze through
Fresh Water3–10Drain tank, bypass heater, pump antifreeze
Holding Tank1–3Pump out, flush, add antifreeze
Livewell / Baitwell0.5–2Drain, pump antifreeze through lines
Shrink Wrap—Frame, wrap, heat-shrink, install vents

What You'll Need

Star Brite Ultimate Aluminum Cleaner & Restorer 64oz

$18-$254.5
View on Amazon

3M Marine Adhesive Sealant 5200 Fast Cure White 3oz

$14-$204.5
View on Amazon

Shoreline Marine Bilge Pump 600 GPH 12V

$15-$254.3
View on Amazon

Star Brite Ultimate Aluminum Cleaner & Restorer 64oz

$18-$254.5
View on Amazon

3M Marine Adhesive Sealant 5200 Fast Cure White 3oz

$14-$204.5
View on Amazon

Shoreline Marine Bilge Pump 600 GPH 12V

$15-$254.3
View on Amazon

As an Amazon Associate, we earn from qualifying purchases.

Frequently Asked Questions

Q

How much antifreeze do I need to winterize my boat?

A typical 26 ft boat with a sterndrive engine needs about 15–20 gallons of non-toxic propylene glycol antifreeze. This covers the engine cooling system, fresh water plumbing, hot water heater, and holding tank lines.

  • Engine (sterndrive): 3.0 gallons to flush cooling system
  • Fresh water system: 3–10 gallons depending on tank size and plumbing length
  • Hot water heater: the full tank capacity (typically 6 gal) plus lines
  • Holding tank: 1–3 gallons to protect macerator and discharge lines
  • Always use marine-grade propylene glycol, NEVER automotive ethylene glycol
Engine TypeCoolant (gal)Typical Boat Size
Small Outboard1.5Under 20 ft
Large Outboard2.520–30 ft
Sterndrive3.020–32 ft
Inboard Gas4.028–40 ft
Inboard Diesel5.030–60 ft
Q

What is the difference between -50F and -100F antifreeze?

Pre-diluted -50°F antifreeze is ready to use and protects down to fifty degrees below zero, suitable for most northern climates. Concentrate -100°F antifreeze can be diluted for mild climates or used full-strength for extreme cold.

  • -50°F pre-mixed: ready to pour, ~$12/gallon, covers most US climates
  • -100°F concentrate: $18/gallon, dilute 50/50 for -50°F protection
  • Full-strength -100°F for Alaska, northern Canada, extreme mountain areas
  • Both must be non-toxic propylene glycol (pink) for marine use
  • Ethylene glycol (green automotive antifreeze) is toxic and contaminates waterways
Q

How much shrink wrap do I need for my boat?

Shrink wrap material covers the top area (length × beam) plus the sides (perimeter × height, about 8 ft including overlap). A 26 ft boat with 9 ft beam needs roughly 794 sq ft of 7-mil shrink wrap, or one standard roll.

  • Top area: boat length × beam = 26 × 9 = 234 sq ft
  • Side area: perimeter × 8 ft height = 70 × 8 = 560 sq ft
  • Total: 234 + 560 = 794 sq ft for a 26 ft boat
  • Standard roll: 17 ft × 110 ft = 1,870 sq ft (~$350/roll)
  • Install 2–4 ventilation holes to prevent mold and condensation
Boat LengthWrap Sq FtRollsMaterial Cost
20 ft5601$350
26 ft7941$350
35 ft1,1081$350
45 ft1,4761$350
Q

Can I winterize my boat myself or should I hire a professional?

DIY winterization costs $100–$300 in materials and takes 3–6 hours. Professional winterization costs $300–$800 depending on boat size and systems. DIY is straightforward for outboard boats but more complex for inboard engines with closed cooling systems.

  • DIY outboard: easiest, flush and fog engine, drain water systems
  • DIY sterndrive: moderate, must drain manifolds and risers completely
  • DIY inboard: harder, closed cooling requires draining block and heat exchangers
  • Professional cost: $300–$500 for standard winterization, +$200–$300 for shrink wrap
  • Most boatyards include haul-out, wash, and storage in a package deal
Q

What happens if I do not winterize my boat?

Water trapped in the engine block, manifolds, water lines, and tanks will freeze and expand, cracking metal and plastic components. A cracked engine block alone costs $3,000–$8,000 to replace. Frozen water heaters and holding tanks can split seams.

  • Cracked engine block: $3,000–$8,000 repair or replacement
  • Cracked exhaust manifolds: $500–$2,000 per manifold
  • Burst water lines and fittings: $200–$1,000 in damage
  • Split water heater tank: $300–$800 replacement
  • Mold from trapped moisture: $500–$3,000 cleanup and remediation

Example Calculations

126 ft Sterndrive Cruiser

Inputs

Engine TypeSterndrive
Engines1
Fresh Water Tank30 gal
Hot Water Heater6 gal
Holding Tank15 gal
Boat Dimensions26 ft × 9 ft

Result

Total Antifreeze15.8 gallons
Engine3.0 gal
Water System10.0 gal
Holding Tank2.8 gal
Shrink Wrap794 sq ft (1 roll)

Engine: 3.0 gal. Water system: 30 × 0.1 + 6 + 1.0 = 10.0. Holding: 15 × 0.15 + 0.5 = 2.75. Total: 3.0 + 10.0 + 2.75 = 15.75 gal. Wrap: 26×9 + 2(26+9)×8 = 234 + 560 = 794 sq ft.

235 ft Twin Outboard Center Console

Inputs

Engine TypeOutboard 150+ HP
Engines2
Fresh Water Tank20 gal
Hot Water Heater0 gal
Holding Tank10 gal
Livewell25 gal
Boat Dimensions35 ft × 11 ft

Result

Total Antifreeze13.5 gallons
Engines (2)5.0 gal
Water System3.5 gal
Holding Tank2.0 gal
Livewell3.0 gal
Shrink Wrap1,121 sq ft (1 roll)

Engines: 2.5 × 2 = 5.0. Water: 20 × 0.1 + 0 + 1.5 = 3.5. Holding: 10 × 0.15 + 0.5 = 2.0. Livewell: 25 × 0.1 + 0.5 = 3.0. Total: 5.0 + 3.5 + 2.0 + 3.0 = 13.5 gal. Wrap: 35×11 + 2(35+11)×8 = 385 + 736 = 1,121 sq ft.

Formulas Used

Total Antifreeze Volume

Total = Engine + Water System + Holding Tank + Livewell

Sums the antifreeze needed for each boat system that holds water.

Where:

Engine= Cooling system capacity (1.5–5.0 gal by engine type)
Water System= Fresh water tank fraction + hot water heater + plumbing lines
Holding Tank= 15% of tank capacity + 0.5 gal for macerator lines
Livewell= 10% of capacity + 0.5 gal for pump lines (if equipped)

Shrink Wrap Area

Area = (L × B) + 2(L + B) × H

Calculates total shrink wrap material from boat dimensions and wrap height.

Where:

L= Boat length in feet
B= Boat beam in feet
H= Wrap height including overlap (typically 8 ft)

Complete Boat Winterization Guide

Winterizing your boat protects its engine, plumbing, and structure from freeze damage during cold months. The two most important steps are running non-toxic propylene glycol antifreeze through every water system and covering the boat with shrink wrap or a quality fitted cover to prevent moisture buildup.

Engine winterization varies by type. Outboards need flushing and fogging. Sterndrives require draining the exhaust manifolds and risers in addition to running antifreeze through the raw-water side. Inboard engines with closed cooling systems need both the freshwater coolant and raw-water circuits addressed.

Shrink wrap provides the best winter protection because it creates a tight, waterproof barrier that sheds snow and ice. Always install ventilation holes and a support structure (poles or strapping) to prevent pooling. Budget about $350 per roll of 7-mil wrap, which covers boats up to 35–40 feet.

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Last Updated: Mar 25, 2026

This calculator is provided for informational and educational purposes only. Results are estimates and should not be considered professional financial, medical, legal, or other advice. Always consult a qualified professional before making important decisions. UseCalcPro is not responsible for any actions taken based on calculator results.

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