How it works
Each liquid is converted from volume to weight using a fixed density, then everything is added up:
Water weight = gallons × 8.34 lb (1 L ≈ 1 kg)
Propane weight = gallons × 4.2 lb + cylinders × rated propane weight
Loaded RV = RV weight + cargo + water + propane
Portable DOT cylinders are named by the propane they hold, so a full 20 lb cylinder adds 20 lb of propane. If you enter your RV’s GVWR, the total is checked against it: 90% or more is shown as at the limit.
Worked example
A travel trailer weighs 6,200 lb without liquids, carries 800 lb of gear, a full 40-gallon fresh tank and two full 20 lb cylinders. GVWR is 7,800 lb.
- Fresh water: 40 × 8.34 = 333.6 lb
- Propane: 2 × 20 = 40 lb
- Loaded RV: 6,200 + 800 + 333.6 + 40 = 7,373.6 lb, about 95% of GVWR.
Traveling with the fresh tank one-quarter full would save about 250 lb.
Water weight chart
| Gallons | Liters | Weight (lb) | Weight (kg) |
|---|---|---|---|
| 10 gal | 38 L | 83 lb | 38 kg |
| 20 gal | 76 L | 167 lb | 76 kg |
| 30 gal | 114 L | 250 lb | 113 kg |
| 40 gal | 151 L | 334 lb | 151 kg |
| 50 gal | 189 L | 417 lb | 189 kg |
| 60 gal | 227 L | 500 lb | 227 kg |
| 75 gal | 284 L | 626 lb | 284 kg |
| 100 gal | 379 L | 834 lb | 378 kg |
Propane cylinder chart
Propane contents of a full cylinder. Add the empty cylinder (tare) weight stamped on the collar for the total.
| Cylinder | Propane (lb) | Propane (kg) | Gallons |
|---|---|---|---|
| 20 lb | 20 lb | 9.1 kg | 4.8 gal |
| 30 lb | 30 lb | 13.6 kg | 7.1 gal |
| 40 lb | 40 lb | 18.1 kg | 9.5 gal |
| 100 lb | 100 lb | 45.4 kg | 23.8 gal |
Where the liquid weight goes
Tank location matters as much as the total. A fresh tank ahead of a travel trailer’s axles raises tongue weight; one behind them lowers it and can cause sway. On a fifth wheel, front tanks add to pin weight and therefore to the truck’s payload. After filling up, recheck with the tongue weight calculator or thepin weight calculator.
Common mistakes
- Assuming dry weight includes water. It almost never does.
- Forgetting the water heater. A 6 to 10 gallon heater holds 50 to 85 lb of water when full.
- Leaving gray and black tanks full. Dump before you drive whenever you can.
- Counting propane cylinders as 20 lb total. The full cylinder weighs closer to 37 lb with the steel tank.
- Stopping at GVWR. Also check the tow vehicle with the GCWR calculator.