liminfoSoil pH Calculator
Free web tool: Soil pH Calculator
Amendment
Lime
Rate (lbs/1000 sq ft)
3.5
Total Amount
17.5 lbs
pH Reference
| pH Range | Level |
|---|---|
| < 5.0 | Very Acidic |
| 5.0 - 5.5 | Acidic |
| 5.5 - 6.0 | Slightly Acidic |
| 6.0 - 7.0 | Optimal |
| 7.0 - 7.5 | Slightly Alkaline |
| 7.5 - 8.0 | Alkaline |
| > 8.0 | Very Alkaline |
Clay soils require more amendment due to higher buffering capacity. Apply lime/sulfur in multiple applications for changes greater than 1.0 pH unit.
About Soil pH Calculator
The Soil pH Calculator helps gardeners, farmers, and agronomists determine how much lime (to raise pH) or sulfur (to lower pH) is needed to bring soil from its current pH to a desired target. Enter the current soil pH, target pH, soil type (sand, loam, or clay), and the area of land in square feet or square metres, and the calculator instantly shows the recommended amendment type, the application rate in pounds per 1,000 square feet, and the total amendment weight required.
Soil type has a major influence on amendment requirements because buffering capacity differs between soil textures. Sandy soils have low buffering capacity and require less lime or sulfur per pH unit of change (lime factor 2 lbs/1,000 sq ft per pH unit). Loam soils are intermediate (lime factor 3.5). Clay soils have high buffering capacity due to their large surface area and cation exchange capacity, requiring the most amendment (lime factor 5). The sulfur factors follow the same pattern at lower rates. For changes greater than 1.0 pH unit, the tool advises splitting the application across multiple seasons to avoid over-correction.
A pH reference table is displayed alongside the results, showing the classification of pH ranges from Very Acidic (< 5.0) to Very Alkaline (> 8.0). The optimal range for most vegetables and lawn grasses is 6.0–7.0. All calculations run in the browser with no data transmitted to any server, making it safe and private for use in professional agricultural planning.
Key Features
- Calculates lime (to raise pH) or sulfur (to lower pH) amendment based on soil type
- Three soil texture options: sand, loam, clay — each with calibrated buffering factors
- Area input supports both square feet (sq ft) and square metres (sq m) with automatic conversion
- Shows amendment type, rate per 1,000 sq ft, and total pounds needed
- Real-time detection: displays "no amendment needed" when current pH equals target
- pH reference table showing 7 acidity/alkalinity classifications (Very Acidic to Very Alkaline)
- Advisory note on split-application for changes greater than 1.0 pH unit
- 100% client-side — no data sent to server, safe for confidential farm planning
Frequently Asked Questions
Why does soil pH matter for plants?
Soil pH controls the availability of nutrients. At pH 6.0–7.0, most essential nutrients (nitrogen, phosphorus, potassium, calcium, magnesium) are at their maximum availability. Below pH 5.5, manganese and aluminum become soluble at toxic levels. Above pH 7.5, iron, zinc, and manganese become unavailable, causing deficiency symptoms even if these elements are present in the soil.
How does lime raise soil pH?
Agricultural lime (calcium carbonate, CaCO₃) neutralises soil acidity by reacting with hydrogen ions (H⁺): CaCO₃ + 2H⁺ → Ca²⁺ + H₂O + CO₂. This raises pH by removing free H⁺ from the soil solution. Dolomitic lime (CaMg(CO₃)₂) also supplies magnesium. Ground limestone takes several months to fully react, especially in dry conditions.
How does sulfur lower soil pH?
Elemental sulfur is oxidised by soil bacteria (Thiobacillus) to sulfuric acid: S + 1.5O₂ + H₂O → H₂SO₄. The sulfuric acid then reacts with soil minerals to release H⁺ ions, lowering pH. This process is slow (weeks to months) and works best in warm, moist soils with high microbial activity. Aluminum sulfate acts faster but can be toxic in excess.
Why does clay soil need more lime than sandy soil?
Clay soil has a much higher cation exchange capacity (CEC) — the ability to hold and buffer cations like H⁺. When lime is added, it must first satisfy the buffering capacity of the soil before pH rises in the soil solution. Clay particles and organic matter both increase CEC, so more lime is needed per pH unit of change. Sandy soils have low CEC and respond quickly to small lime applications.
How do I measure my soil pH before using this calculator?
Soil pH can be measured with a digital pH meter probe, a soil test kit with color-matching solution, or through a lab soil analysis service. For the most accurate results, collect samples from multiple spots in the area, mix them together, and test the combined sample. pH meters should be calibrated with buffer solutions (pH 4.0 and 7.0) before use.
What is the optimal soil pH for common garden plants?
Lawns and most vegetables prefer pH 6.0–7.0. Blueberries and azaleas thrive in acidic soil at pH 4.5–5.5. Potatoes prefer slightly acidic pH 5.0–6.0 to reduce scab disease. Brassicas (cabbage, broccoli) grow best at 6.5–7.0 and benefit from liming to reduce clubroot disease. Turf grasses generally perform best at pH 6.0–6.5.
How long does it take for lime to change soil pH?
Agricultural lime typically takes 3–6 months to raise pH noticeably, and up to 2 years to reach maximum effect. Finely ground lime reacts faster than coarsely ground. Lime works faster in moist, warm conditions and when thoroughly incorporated into the soil by tilling. For vegetable gardens, apply lime in autumn to allow reaction before the spring planting season.
Can I over-apply lime or sulfur?
Yes. Over-liming (pH above 7.5) causes micronutrient deficiencies, particularly iron, manganese, and zinc chlorosis. Over-acidifying with sulfur below pH 5.0 causes aluminum toxicity and reduces beneficial soil bacteria populations. Always test soil pH before and after amendment, and apply in multiple smaller doses for changes greater than 1 pH unit, as advised in the calculator.