Soil pH Amendment Calculator (Lime / Sulfur)
Estimate how much lime or elemental sulfur to apply to move your soil from its current pH to a target, by soil texture and area. Runs in your browser.
Lime raises pH (makes soil less acidic).
Rates are typical extension-service figures (lb per 100 ft² per pH unit) and vary with soil texture and organic matter — sandy soils need less, clay more. Apply in split doses, work into the topsoil, and retest after a few months; pH change is gradual (lime takes months). For best accuracy, get a lab soil test with a buffer-pH recommendation. Not a substitute for a soil test.
About this tool
Soil pH controls how well plants can take up nutrients, and most vegetables and lawns prefer a slightly acidic 6.0–7.0. To raise pH (reduce acidity) you add lime; to lower it (increase acidity, as blueberries and azaleas like) you add elemental sulfur. How much depends on how far you are moving the pH, the area, and crucially the soil's texture: sandy soils have little buffering and shift easily, while clay and high-organic soils resist change and need substantially more. This calculator applies typical university-extension application rates — pounds of amendment per 100 square feet per unit of pH change — for sandy, loam, and clay soils, picks lime or sulfur based on whether you are raising or lowering pH, and scales to your area. Two important cautions it states plainly: pH change is slow (lime can take months to fully act), so apply in split doses, work it into the topsoil, and retest before adding more; and for real accuracy a lab soil test with a buffer-pH recommendation beats any rule of thumb. Everything runs in your browser.
How to use it
- Enter your current soil pH (from a test) and your target pH.
- Select your soil texture — sandy, loam, or clay.
- Enter the area to treat in square feet.
- Read the amount of lime or sulfur to apply, then retest after a few months.
Frequently asked questions
- Do I add lime or sulfur?
- Lime to raise pH (make acidic soil more neutral/alkaline); elemental sulfur to lower pH (make soil more acidic). The calculator picks the right one automatically based on whether your target is above or below your current pH.
- Why does soil texture change the amount so much?
- Texture and organic matter determine buffering capacity — how strongly the soil resists pH change. Sandy soils have low buffering and move with little amendment; clay soils have high buffering and need considerably more for the same pH shift.
- How long until the pH actually changes?
- Slowly. Ground limestone can take several months to fully react, and sulfur depends on soil microbes and temperature. Apply in advance of the growing season, water it in, and retest before applying more — over-applying based on no change yet is a common mistake.
- Should I apply it all at once?
- For large changes, split the application (for example half now, half a few months later) and work it into the top several inches rather than leaving it on the surface. This avoids overshooting and gives a more even result.
- How accurate is this estimate?
- It uses standard extension rates and is a good planning figure, but actual need varies with your specific soil chemistry and organic matter. A lab soil test that reports a buffer pH gives a precise lime recommendation — use it for important plantings.
- Is this a substitute for a soil test?
- No. You need a measured current pH to use it sensibly, and a full soil test gives the most reliable amendment recommendation. This tool estimates the quantity once you know your pH and target.