Three grades of the same salt, carrying 20%, 16% and 9.8% magnesium. The gap between the strongest and the weakest is more than double.
The short answer. On our published grades: anhydrous 20% Mg, monohydrate 16% Mg, heptahydrate 9.8% Mg, 13% S. A kilogram of the anhydrous grade carries roughly twice the magnesium of a kilogram of the heptahydrate, so the three cannot be priced against one another per kilogram of bag.
The difference is water of crystallisation and nothing else about the magnesium sulphate itself. The anhydrous grade carries none, the monohydrate one molecule, the heptahydrate seven. Each molecule of water is weight in the bag that is not magnesium.
The heptahydrate is the grade most people picture when they hear magnesium sulphate. It is also the weakest of the three by magnesium content, which is why buyers who move material over any distance often look at the monohydrate or the anhydrous grade instead.
| Product | Formula | Grade published | Standard packing |
|---|---|---|---|
| Magnesium Sulphate Anhydrous | MgSO₄ | 20% Mg | 50 kg net, HDPE bag |
| Magnesium Sulphate Monohydrate | MgSO₄·H₂O | 16% Mg | 50 kg net, HDPE bag |
| Magnesium Sulphate Heptahydrate | MgSO₄·7H₂O | 9.8% Mg, 13% S | 50 kg net, HDPE bag |
Every grade in this table is the figure published on that product’s own page on this site. Nothing is estimated. The guaranteed analysis on the product page and the batch certificate of analysis govern any supply.
Our heptahydrate page publishes 13% S alongside the magnesium. Where a published grade carries a second figure like that, it is because the product page states it. Where a page does not state a figure, we have not put one here rather than infer it. If a parameter matters to your process, ask and we will confirm it against the batch certificate of analysis.
Where two products carry the same element at different strengths, the price per kilogram of bag is not a comparison. Divide the delivered price per kilogram by the element fraction and you get the cost per kilogram of the thing you are actually buying. That is the only basis on which grades of different strength can be set against each other.
Our nutrient cost comparison calculator does that arithmetic on any two products in our range and prints its working, and the element content calculator converts between kilograms of product and kilograms of the element. Freight follows the same logic: moving a weaker grade means paying to move more material that is not the element.
That is decided by your process, and by things we cannot see from here: how the product is applied, what it is blended with, what has to dissolve and how fast, the specification you or your customer must meet, and how far the material travels. Any supplier who answers that question without asking about your process is guessing.
We manufacture the alternatives set out above, so we have no reason to steer you toward the dearer one. Describe the application and we will tell you what we would send and why, including when the cheaper grade is the right answer.
Four things let us price these products without a round of questions: the grade, the quantity, the delivery location, and any specification you have to meet. Send those and we come back with a price, the packing, and the documents that travel with the consignment. There is more detail on what to send us for a quote.
Know what you need already? Send the grade, the quantity and the delivery location and we will quote against them.
Send the grade, the quantity and the delivery location and we will quote against them.