Gypsum Application Calculator Guide
Use this gypsum application calculator to estimate pounds of gypsum for improving clay soil structure and drainage. Enter garden area in square feet and application rate in pounds per 1,000 sq ft to plan broadcast spreading.
How to use the gypsum application calculator
Enter total garden or lawn area in square feet and your target application rate in pounds per 1,000 square feet.
The result is total gypsum weight in pounds for one broadcast application at that rate.
Gypsum application formula
Total gypsum (lbs) = (Area ÷ 1,000) × Application rate (lbs per 1,000 sq ft).
Gypsum (calcium sulfate) supplies calcium and sulfur without significantly changing soil pH — it helps disperse sodium and improve flocculation in sodic or heavy clay soils.
- Total lbs = (area / 1000) × rate
- Common rates: 20–40 lbs per 1,000 sq ft for garden clay
- Agricultural gypsum is not the same as drywall scrap — use labeled soil products
- Effects build over months — not an instant fix
Worked example
A 1,000 sq ft vegetable garden on heavy clay with a recommended rate of 40 lbs per 1,000 sq ft.
Total gypsum = (1000 ÷ 1000) × 40 = 40 lbs broadcast and incorporated into the top 6–8 inches.
When gypsum helps
Gypsum benefits compacted clay, sodic soils (high sodium), and soils low in calcium. It does not replace organic matter, aeration, or drainage fixes in waterlogged beds.
A soil test showing sodium or calcium imbalance guides whether gypsum is appropriate.
Application tips
Spread evenly with a broadcast spreader and incorporate lightly. Pair with compost for lasting structure improvement. Irrigate after application to move calcium into the root zone.
- Do not expect gypsum to acidify soil — use sulfur for that.
- See soil pH adjustment calculator for lime or sulfur needs.
- Combine with soil amendment calculator for compost quantities.
- Re-evaluate structure after one growing season before reapplying.