Lime Application Calculator
Reads a two-way soil texture by pH table for pounds of lime per 1,000 sq ft, then sizes total pounds and bags for your area.
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Gypsum Application Calculator
Reads a texture-by-purpose table for gypsum pounds per 1,000 sq ft, then converts your area into bags, calcium and sulfur, split by pass.
Gypsum Application Calculator
Chlorova · updated for 2026
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Rates are the extension turf and landscape ranges for gypsum as a calcium source, and a soil test with sodium percentage, SAR or a Ca:Mg ratio overrides any table for these purposes. Gypsum is not lime: it does not raise pH in neutral soils, so anyone hoping to correct acidity should use lime and its own rate table instead. Sodic land reclamation is a two-part job, because displaced sodium has to be washed below the root zone with deliberate extra watering, which means good drainage is a condition of success rather than a nice extra.
Gypsum is the most mis-sold soil amendment in the garden aisle, bought as a cure for compaction and promised as a pH raiser it cannot perform. What calcium sulfate actually does is trade calcium onto clay surfaces, flocculate the mess, and add plant-available calcium and sulfur without shifting pH at all. The right rate depends on how heavy your soil is and which of four genuinely different jobs you are asking it to do. This calculator reads a texture-by-purpose table, converts the result to your area, and reports the bags, the nutrient credit and the split.
Getting From Table to Bags
- Choose the texture your soil actually is, not the one you wish for.
- Pick the reason you are spreading, which sets the rate column.
- Confirm the reading with a soil test when sodium is suspected.
- Measure the area in square feet, beds and lawn together.
- Set the bag size printed on the product at the store.
- Split heavy rates across two or three passes if advised.
- Read the pounds needed before you load the spreader.
- Check the calcium and sulfur credit against your fertility plan.
- Water the surface in after each pass to start the reaction.
- Re-test the following season rather than re-guessing the rate.
Two Keys In, Pounds Out
The rate is a two-key lookup: soil texture across, purpose down, returning pounds per 1,000 square feet, anywhere from 4 lb for sandy-soil maintenance with sodic water to 50 lb for heavy clay sodicity reclamation. Area scales it the way every lawn product works, so 2,000 square feet at a 50 lb table rate is 100 lb of material and three 40-lb bags, with a ceiling function because a store does not sell two thirds of a bag.
The nutrient lines are simple chemistry rather than product claims. Gypsum is calcium sulfate dihydrate, about 23% calcium and 19% sulfur by weight, so 100 lb of it carries roughly 23 lb of calcium and 19 lb of sulfur into the root zone. Those numbers matter when a soil test is already recommending calcium, because they let gypsum count toward the requirement instead of being applied blindly on top of it.
Worked Example: Sodic Clay Under Two Thousand Feet
- Soil test flags dispersive clay, so texture is clay and purpose is sodicity.
- The table reads 50 lb per 1,000 sq ft for that pairing.
- Your lawn and beds total 2,000 sq ft to treat.
- So 50 times 2,000 divided by 1,000 gives 100 lb of gypsum.
- At 40 lb per bag, ceil lands on three bags at the store.
- Split over two passes, each goes down at 50 lb.
- The calcium credit reads 23.3 lb, sulfur 18.6 lb total.
- That is a per-square-foot rate of 0.05 lb, a heavy blanket.
- The verdict line calls it reclamation class, split and leach.
- Watering after each pass is what moves sodium below the roots.
- A follow-up test next season decides whether to repeat it.
Pounds per 1,000 Sq Ft
The table behind the calculator, expressed as the extension ranges for gypsum use on lawns and landscape beds. Rates are per application season, and the sodium column is the one that most often needs splitting across passes along with deliberate leaching water.
| Texture | Structure | High sodium | Calcium deficit | Sodic water |
|---|---|---|---|---|
| Sand | 5 | 20 | 10 | 4 |
| Loam | 8 | 30 | 15 | 6 |
| Silt loam | 8 | 35 | 15 | 6 |
| Clay loam | 12 | 40 | 20 | 8 |
| Clay | 15 | 50 | 25 | 10 |
Key Terms
- Gypsum
- Calcium sulfate dihydrate, a neutral salt that supplies Ca and S without changing pH.
- Flocculation
- Clay particles binding into crumbs when calcium replaces sodium on their surfaces.
- ESP
- Exchangeable sodium percentage, the lab measure of a sodically dispersed soil.
- SAR
- Sodium adsorption ratio of irrigation water, a measure of how much sodium it will leave behind.
- Leaching
- Applying extra water to move displaced sodium below the root zone.
Where the Advice Gets Honest
- Gypsum will not raise pH the way lime does, so using it to correct acidity in a garden bed is the single most common purchase error in the amendment aisle.
- Compaction caused by traffic is a physical problem, and gypsum only helps when dispersion is the cause, which is why a crust that breaks under a fork responds and a wheel-rut pad does not.
- Sodic reclamation is measured in inches of leaching water, not pounds of product, because the displaced sodium has to leave the profile somewhere and a flat, poorly drained bed keeps it.
- The calcium and sulfur credit is a real fertility number, so on a soil test already showing adequate calcium, a structure pass is buying physical improvement rather than nutrition.
- Effects are gradual and seasonal: flocculation shows up as better wetting and less crusting over a year or two, and any product promising same-week soil change is selling hope.
Common Mistakes & Fixes
- Spreading gypsum to fix acidic soil because the bag looked like lime.
- Treating a compacted, walked-on pad with calcium instead of aeration.
- Applying a reclamation rate on clay with nowhere for the sodium to go.
- Leaving gypsum on the surface without watering it into the profile.
- Doubling the rate for a faster result and burning a seedling bed.
- Guessing texture from feel rather than confirming with a test.
- Re-applying annually for sodic water without rechecking the water report.
When to Use This (and When Not To)
Use it when a soil test or a very obvious crust points at sodium, dispersion or a calcium shortfall, and when irrigation water reports a high SAR. Leave it alone if the goal is raising pH, which belongs to the lime-application calculator, and use the soil-amendment calculator for compost and bulk organic work on the same bed.
Gypsum Application Calculator: Frequently Asked Questions
Does gypsum loosen clay soil?
It loosens clay only when sodium or dispersion is what makes the clay tight, because calcium binds the particles into crumbs that water can enter. A clay pad compacted by mowing and foot traffic stays compacted, and needs aeration or a rest season instead.
How many pounds of gypsum per 1,000 square feet?
Between about 5 and 15 lb for structure work, 10 to 25 lb for a calcium deficit, and 20 to 50 lb where sodium is the real problem. Texture drives the number inside those ranges, since sands need less material and clays need more to change anything.
Can I put too much gypsum on?
Yes, and the cost is salt rather than burn-free safety, because gypsum is a salt and heavy single doses can hurt seedlings and steal water from the soil solution. Split large rates into passes and water each one in, which is also cheaper than one enormous application.
Is gypsum the same as lime?
No. Lime is calcium carbonate and raises soil pH, while gypsum is calcium sulfate and supplies calcium without any pH change in a neutral or alkaline soil. Choose lime for acidity and gypsum for sodium, structure or calcium nutrition.
When do I see results after applying gypsum?
Wetting and crusting changes usually show within a season, and sodicity measures change over one to three years once leaching is happening. Anything marketed as a same-week soil overhaul is describing a surface effect rather than real amendment.
Should I work gypsum into the soil?
Where you can, yes, since placing calcium where the clay dispersion actually occurs beats leaving it on a lawn surface waiting for rain. On established turf, apply it as a topdressing and water it in, because disturbing the sod costs more than the incorporation would gain.
Sources & Further Reading
- Gypsum Use for Soil Structural Remediation — University of Florida IFAS Extension. Basis for texture-dependent turf and landscape rates.
- Sodic and Saline Soils: Gypsum and Leaching — USDA Natural Resources Conservation Service. Source of the two-part reclamation requirement.
- Gypsum for Turfgrass — Penn State Extension. Supports the maintenance rate for sodic irrigation water.
Chlorova Gardening Team
Builds, checks and documents every tool we publish
Chlorova editorial review
Checked against extension-service publications
Formula verified against published references · Updated