To calculate gypsum dosage for brewing water: 1 gram of gypsum (calcium sulfate dihydrate) dissolved per liter raises sulfate by approximately 558 mg/L. For example, a 19 L batch targeting a 50 mg/L sulfate increase needs (50 ÷ 558) × 19 ≈ 1.7 g of gypsum.
What's the gypsum dosing formula?
Gypsum's chemical formula is CaSO₄·2H₂O — calcium sulfate dihydrate. By molecular weight, sulfate (SO₄) makes up roughly 55.8% of gypsum, with calcium and water of crystallization accounting for the rest. That gives a direct conversion:
grams of gypsum = (target sulfate increase in mg/L ÷ 558) × batch volume in liters
The same gram of gypsum also raises calcium by roughly 233 mg/L (23.3% of its weight) — a side effect worth tracking if you're also managing mash pH, since calcium is the ion that drives most pH-lowering mineral additions.
Worked example
For a 19 L (5 gal) batch targeting a 50 mg/L sulfate increase for a hop-forward IPA:
(50 ÷ 558) × 19 = 1.7 g of gypsum
| Batch size | Gypsum for +50 mg/L sulfate |
|---|---|
| 4 L (1 gal) | 0.36 g |
| 19 L (5 gal) | 1.7 g |
| 23 L (6 gal) | 2.1 g |
Why sulfate specifically, and not just "more minerals"
Sulfate is the ion most directly linked to how dry and bitter a hoppy beer reads on the palate. Chloride, by contrast, tends to round out malt sweetness and give a fuller mouthfeel. Neither mineral changes actual measured bitterness (IBU) — they shift how the same bitterness is perceived.
A sulfate:chloride ratio of 2:1 or higher is the common target for accentuating hop character in styles like American IPA. Reversing the ratio toward chloride-dominant (closer to 1:2) is more typical for malt-forward styles where a rounder, softer finish is the goal.
Skip the manual math
The beer calculator's Water Chemistry tool applies this formula directly, alongside chloride and calcium tracking for your full mineral profile.
For the full water chemistry picture — including mash pH correction and regional water profile matching — see Home Brewing Science, Chapter 04.
This formula assumes gypsum is dissolved directly into brewing water with no pre-existing sulfate content. Test your source water or use published local water reports to determine your true starting point before adding minerals.