Float Tank Epsom Salt Calculator
Enter your tank volume and target specific gravity to get the exact kilograms of Epsom salt to dissolve. Includes saturation check, 25 kg bag count, and magnesium concentration. Nothing uploaded.
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Learn more: floating and Epsom salt density
How much salt a float needs
A float tank works because the water is dense enough to hold you up. Wikipedia's isolation tank entry describes a tank filled with about 25 centimeters (10 inches) of water at around 35 degrees C, with enough dissolved Epsom salt for a specific gravity of approximately 1.25 to 1.26.
The calculator turns your target specific gravity (SG) into a salt concentration using a measured density table for magnesium sulfate solutions. It converts that to Epsom salt, which is the heptahydrate form. Water of crystallization makes up about 51% of its weight, so only 48.8% is anhydrous magnesium sulfate.
A worked example
For an 800 litre tank at SG 1.28 and 35 degrees C, the solution needs about 323 g of anhydrous magnesium sulfate per litre. Divided by 0.488, that is 661 g of Epsom salt per litre, or about 529 kg in total, which is 22 bags of 25 kg.
The tank volume is the final volume of solution, so dissolve the salt and then top up to that volume. Raising the target to SG 1.30 takes about 570 kg for the same tank.
The saturation limit
Wikipedia gives the solubility of anhydrous magnesium sulfate as 35.1 g per 100 mL of water at 20 degrees C, 26.9 at 0 degrees and 50.2 at 100 degrees. The calculator uses that to find the strongest solution possible at your water temperature.
At 35 degrees C that limit is about 360 g of anhydrous salt per litre. SG 1.30 needs 348 g, just under it, while SG 1.32 is over and gets a warning. Extra salt past saturation settles on the bottom without raising the density.
FAQ
Why does the specific gravity matter for a float?
Density decides how high you sit in the water. The denser the solution, the more of your body stays above the surface without effort, which is why the target SG is the main input.
How does a float tank compare with the Dead Sea?
The calculator's Dead Sea preset is SG 1.24, a little below the 1.25 to 1.30 range used for tanks. A tank holds a small volume, so it is practical to make it much denser.
Can I use table salt?
No. This calculator and its density table are for Epsom salt, magnesium sulfate. Other salts have different densities and solubility, so the salt amounts it gives do not apply to them.