RV Water Tank Size Calculator

Understanding RV Water Tank Sizes

Whether you are buying a new RV, building a custom van conversion, or preparing for an extended off-grid boondocking trip, understanding exactly how much water you need is critical. Running out of fresh water—or worse, overfilling your black tank—can ruin a camping trip fast.

Fresh, Gray, and Black Tanks Explained

• Fresh Water Tank: Holds your clean, potable water. You use this for drinking, cooking, showering, and flushing the toilet. Your fresh tank size determines how long you can camp without hookups.
• Gray Water Tank: Collects "dirty" water from your sinks and shower. It fills up almost as quickly as you deplete your fresh water. If your gray tank fills up, water will back up into your shower pan.
• Black Water Tank: Strictly for toilet waste. This tank requires chemicals to break down waste and control odors. Black tanks usually fill much slower than gray tanks.

How to Conserve Water While Boondocking

If your current RV tanks are smaller than the calculator recommends, you don't necessarily need to cut your trip short. You just need to adopt water-saving techniques:

• Master the "Navy Shower": Turn the water on just to get wet. Turn it off at the showerhead valve while you lather up with soap and shampoo. Turn it back on only to rinse. This can reduce shower usage from 5 gallons down to 1.5 gallons per person.
• Use Wash Basins for Dishes: Instead of washing under a running faucet, use two plastic tubs. Fill one with soapy water for washing, and a second with clean water for dipping and rinsing. Better yet, use a spray bottle to wipe heavily soiled plates outdoors.
• Bring Separate Drinking Water: Bringing 5-gallon jugs or a case of bottled water directly removes the drinking and cooking burden from your main fresh tank.
• Use Public Restrooms: If camping near pit toilets or visitor centers, using their facilities drastically reduces black tank fill rates.

The Weight Factor

Many smaller travel trailers and Class B vans have limited Cargo Carrying Capacity (CCC). Always check your payload limits before driving with full water tanks. It is common practice to travel with empty or slightly filled tanks and fill up at a gas station or ranger station close to your boondocking destination to save on gas mileage and wear-and-tear on your vehicle's suspension.

Common RV Tank Capacities (Industry Standard Averages)