DIY Sea Salt & Magnesium Bath Ratio Scaler

How it works

The scaler multiplies your bath volume by a grams-per-litre rate. Epsom salt uses 1.5 g per litre for mild, 2.5 g for standard, and 4.0 g for strong. Sea salt uses slightly lower rates — 1.0 g, 2.0 g, and 3.0 g per litre — because it is usually used as a gentler soak and dissolves with other minerals present.

For a mix, the rates are halved and combined: half the Epsom rate plus half the sea-salt rate. So a standard 150-litre mixed bath needs 338 g in total, made up of 188 g of Epsom salt (1.25 g per litre) and 150 g of sea salt (1.0 g per litre). Weigh the salts on kitchen scales rather than relying on cups, which vary a lot between brands and grain sizes.

Safety notes: keep the concentration at or below 5 g per litre, which is well above the strong rates here, and do not try to make a stronger bath by adding extra scoops on top. Soak for 15–20 minutes, keep the water comfortably warm rather than hot, and rinse with fresh water afterwards. Avoid salt baths on broken, sunburnt, or irritated skin, and be cautious if you have eczema, psoriasis, or any skin condition that flares with salt or heat. If you are pregnant, or managing a heart, kidney, blood pressure, or skin condition, talk to a clinician before using salt baths.

How to use your result

Dissolve the weighed salt in warm running water, stirring until most of it has disappeared before you get in. If any grains remain on the bath floor, they can feel gritty underfoot, so give them a minute longer to dissolve. Start with the mild strength for a first bath and only move up if your skin feels comfortable afterwards.

Related guides

• Epsom Salt vs Sea Salt Baths, Compared
• DIY Magnesium Bath Recipes and Ratios
• Home Spa Bath Safety and Skin Care