A standard cast iron tub weighs between 300-500 lbs (136-227 kg) empty.
Cast iron tubs are heavy due to their durable enamel-coated iron construction. Weight varies by size: alcove tubs average 300-400 lbs, while freestanding clawfoot models can exceed 500 lbs. Always check manufacturer specs, as dimensions and thickness impact total weight.
Why Cast Iron Tubs Are Heavy
- Material density: Cast iron is thicker and denser than acrylic or fiberglass.
- Enamel coating: Adds 10-20 lbs for durability and gloss.
- Reinforcement: Some models include steel or extra bracing for stability.
- Size matters: Longer/deeper tubs (e.g., 60" vs. 54") weigh significantly more.
Weight Comparison by Tub Type
| Tub Type | Average Weight (Empty) | Typical Dimensions | Installation Notes |
|---|---|---|---|
| Alcove (3-wall) | 300-400 lbs (136-181 kg) | 54"-60" L × 30"-32" W × 14"-16" D | Requires reinforced flooring; often paired with tile surround. |
| Freestanding (clawfoot) | 400-500+ lbs (181-227+ kg) | 55"-72" L × 28"-36" W × 20"-24" D | Needs floor-mounted support; legs add ~10 lbs each. |
| Drop-in/Undermount | 350-450 lbs (159-204 kg) | 60"-72" L × 32"-42" W × 16"-20" D | Installed in a deck or platform; weight distributed across frame. |
Factors That Affect Weight
- Length: Every additional 6" can add 20-40 lbs.
- Thickness: High-end tubs have thicker iron (up to ¼") for heat retention.
- Water capacity: Filled, a tub gains 500-800 lbs (water weighs ~8.3 lbs/gallon).
- Accessories: Built-in armrests, jets, or overflow drains add 5-15 lbs.
Weight vs. Other Tub Materials
- Acrylic: 50-100 lbs (lightweight but less durable).
- Fiberglass: 70-120 lbs (prone to flexing/scratched).
- Stone resin: 200-300 lbs (heavy but not as dense as cast iron).
- Copper: 150-250 lbs (expensive, requires polishing).
Installation Considerations
- Flooring: Reinforce joists if weight exceeds 40 lbs/sq ft (consult a structural engineer).
- Placement: Position near load-bearing walls to distribute weight.
- Moving: Requires 2-4 people or a dolly; protect floors with plywood.
- Drainage: Ensure plumbing supports the tub's static + dynamic (water) weight.
How to Weigh Your Specific Tub
- Check the manufacturer's spec sheet (model number often on the underside).
- Use a bathroom scale under each foot (add results for total weight).
- For filled weight: Add 8.3 lbs per gallon of water (e.g., 50-gallon tub = +415 lbs).