The whole calculation is a formula weight
There is nothing mysterious in a brewing salt addition. Gypsum is calcium sulfate dihydrate, formula weight 172.16. Of that, 40.08 is the calcium and 96.06 is the sulfate, which makes a gram of gypsum 23.3% calcium and 55.8% sulfate by weight. Dissolve one gram in one US gallon — 3.785 litres — and you have added 0.233 grams of calcium to 3.785 litres, which is 61.5 milligrams per litre, which is 61.5 parts per million. The sulfate comes out at 147.4 ppm by the same division.
Every figure on this page is that arithmetic repeated. It is worth doing from the formula rather than copying a chart, because charts get transcribed wrong and because the anhydrous and hydrated forms of the same compound are different weights. Calcium chloride sold as the dihydrate is 147.01 per formula unit; the anhydrous form is 110.98, and a gram of it carries about a third more calcium. If your product is not labelled with which one it is, the numbers here are wrong for it.
| Salt | Formula | One gram in one gallon |
|---|---|---|
| Gypsum | CaSO4·2H2O | 61.5 ppm calcium, 147.4 ppm sulfate |
| Calcium chloride | CaCl2·2H2O | 72 ppm calcium, 127.4 ppm chloride |
| Epsom salt | MgSO4·7H2O | 26.1 ppm magnesium, 103 ppm sulfate |
| Magnesium chloride | MgCl2·6H2O | 31.6 ppm magnesium, 92.1 ppm chloride |
| Table salt | NaCl | 103.9 ppm sodium, 160.2 ppm chloride |
| Baking soda | NaHCO3 | 72.3 ppm sodium, 191.9 ppm bicarbonate |
Six knobs, and none of them turns one thing
This is the part that catches people. A water profile is six numbers, there are six salts on this page, and it looks like a system you can solve. It is not, because each salt is locked to a fixed ratio between two ions. Reach for gypsum to lift the calcium and you get 2.4 parts of sulfate for every part of calcium whether you wanted them or not. Reach for calcium chloride instead and the same calcium arrives with 1.8 parts of chloride.
So the sulfate to chloride ratio is not something you set independently of calcium — it is decided by which calcium salt you used and in what proportion. The default case makes this concrete: 4 grams of gypsum and 3 grams of calcium chloride in 7 gallons gives 66 ppm calcium, and the sulfate and chloride that came along with it land at 84 and 55, a ratio of about 1.5 to 1. Change the split between those two salts and the calcium can stay exactly where it is while the ratio moves anywhere from all sulfate to all chloride.
The gap-closing section takes this seriously rather than pretending to solve the system. Pick one ion, name the figure you are aiming it at, and it shows the weight of each salt that would close that gap on its own and exactly what else each one drags into the water. That is an honest presentation of a problem with more constraints than degrees of freedom, and it is more useful than a solver that quietly picks a compromise you did not ask for.
What is not here, deliberately
There is no recommended profile on this page, for any beer, any style or any purpose. Water targets are recipe decisions and they belong to whoever wrote the recipe; publishing a set of numbers here for people to apply to beers and systems they were never derived for would be worse than publishing nothing. The calculator takes your figures and does arithmetic on them.
There is also no mash pH calculation, and its absence is not an oversight. Where a mash pH lands is a function of the alkalinity of the water, of the grain bill including how much dark and acidulated malt is in it, and of the buffering capacity of the malt itself, and none of those appear in a list of ion concentrations. Bicarbonate is the ion most closely tied to it, which is exactly why a bicarbonate figure without a grain bill tells you very little. That calculation is a different tool and this page does not approximate it.
Blending down, and the one direction that does not work
Every operation here adds. There is no salt that removes calcium from water, and if your source already carries more of something than you want, the only levers are dilution with water that has less of it — reverse osmosis or distilled water — or starting from that water and building up. Blending is a simple proportion: half and half with zero-ion water halves every figure at once, including the ones you liked.
That asymmetry is the practical argument people make for building from stripped water rather than adjusting tap water, and it is also why the source water fields on this page matter. Entering zeros because you do not have a report does not make the ions go away; it makes the resulting profile wrong by exactly the amount your water already contained.
Questions people ask
How much calcium does one gram of gypsum add?
In one US gallon, 61.5 parts per million of calcium and 147.4 of sulfate. The arithmetic is worth seeing once: gypsum is calcium sulfate dihydrate at 172.16 per formula unit, of which 40.08 is calcium, so a gram is 0.233 grams of calcium; spread through 3.785 litres that is 61.5 milligrams per litre. In litres rather than gallons the same gram gives 232.8 ppm calcium and 557.9 ppm sulfate, which is why the volume unit matters more than any other input on the page.
Which salt should I use to raise calcium?
That question has no answer without knowing what you want the sulfate and chloride to do, because both calcium salts here bring one of them. Gypsum brings sulfate at about 2.4 times the calcium by weight; calcium chloride brings chloride at about 1.8 times. Blending the two lets you land a calcium figure with the sulfate and chloride landing wherever the blend puts them. This page will show you what each choice does and will not choose for you, because the choice belongs to the recipe.
What sulfate to chloride ratio should I aim for?
This page has no opinion on that and does not publish one. It divides your sulfate figure by your chloride figure and reports the result, which is all a ratio is. The number is talked about a great deal and the evidence behind specific values is a good deal thinner than the confidence with which they are quoted. Take a target from the recipe you are brewing or from your own notes on batches you have made, use the calculator to hit it accurately, and record what happened.
Do I add the salts to the mash water or to all of the water?
Whichever you do, enter that volume, and be consistent between batches so your notes mean something. Treating only the mash water concentrates the additions in the mash, which is where the minerals interact with the grain; treating the full volume spreads them across the mash and the sparge. The two produce different mash conditions from the same total weight of salt, which is why a recipe that gives salt weights without saying which volume they are for is under-specified. Ask, or pick one and write it down.
Can I use this to lower an ion that is already too high?
No, and nothing else can either, other than dilution. Every salt here adds; there is no addition that removes calcium, sulfate or anything else from water. If your source carries more of an ion than you want, the options are to blend with reverse osmosis or distilled water, which lowers everything in the same proportion, or to build entirely from stripped water. The calculator shows a negative gap when you are already past your figure so that the situation is visible rather than silently rounded away.