Calculator Inputs
This tool estimates practical garden gypsum amounts. Always compare results with a soil test or local extension recommendation before large applications.
Formula Used
Base gypsum need: Area × selected base rate.
Adjusted pure gypsum rate: Base Rate × Texture Multiplier × Severity Multiplier.
Product rate: Adjusted Pure Gypsum Rate ÷ Purity Fraction.
Total product needed: (Area in ft² ÷ 100) × Product Rate.
Bags required: Total Product Needed ÷ Bag Size, rounded up for purchasing.
Total cost: Rounded Bag Count × Cost Per Bag.
Example: A 600 ft² bed at 20 lb/100 ft², medium severity, clay texture, and 90% purity uses 600 ÷ 100 × (20 × 1.10 × 1.00 ÷ 0.90) = 146.67 lb of product.
How to Use This Calculator
- Choose whether you want to enter dimensions or a direct area.
- Enter the garden size in feet, meters, square feet, square meters, or acres.
- Select the application purpose that best matches your soil problem.
- Adjust texture, severity, product purity, and split applications.
- Enter bag size and price for material planning.
- Press Calculate Gypsum to show the result above the form.
- Review totals, bag count, cost, schedule, and the Plotly graph.
- Use the CSV and PDF buttons to export your result summary.
Example Data Table
| Garden Area | Purpose | Texture | Purity | Estimated Product | Rounded Bags |
|---|---|---|---|---|---|
| 300 ft² | General conditioning | Loam | 95% | 31.58 lb | 1 bag of 40 lb |
| 600 ft² | Clay loosening support | Clay | 90% | 146.67 lb | 4 bags of 40 lb |
| 1,000 ft² | Salt stress support | Sandy | 85% | 150.00 lb | 4 bags of 40 lb |
| 2,000 ft² | Sodic remediation | Heavy clay | 90% | 1,066.67 lb | 27 bags of 40 lb |
Frequently Asked Questions
1) What does gypsum do in a garden?
Gypsum supplies calcium and sulfur. It can also help improve structure in some compacted or sodic soils. It is not a universal fix, so a soil test remains the safest way to confirm whether gypsum fits your site.
2) Does gypsum lower soil pH?
No. Gypsum usually does not change soil pH the way lime or sulfur can. It mainly adds calcium sulfate and may improve infiltration or aggregation under suitable soil conditions.
3) Why does product purity matter?
Lower purity means less actual gypsum in each pound of product. The calculator increases the required product amount when purity drops, helping you estimate a more realistic purchase and spreading plan.
4) Should I apply gypsum all at once?
Large garden projects are often easier to manage in split applications. Dividing the total into smaller passes can improve handling, reduce waste, and align better with watering, bed preparation, or seasonal maintenance.
5) Can gypsum fix every clay soil problem?
Not always. Gypsum may help certain clay or sodium-related issues, but it does not solve every drainage, compaction, or organic matter problem. Compost, aeration, and proper watering may still be necessary.
6) Is the graph useful for small gardens?
Yes. Even in small beds, the graph shows how the total material is divided across applications. That makes spreading, timing, and bag planning easier to understand at a glance.
7) Which rate should I choose first?
Start with the purpose that most closely matches your soil condition. If you already have a lab recommendation, choose the custom rate option and enter the exact amount given by the test.
8) Are the cost values exact?
They are estimates based on rounded bag purchases. Taxes, delivery, waste, and local product size differences can change your final cost, so treat the amount as a planning figure.