Lawn Lime Calculator
Calculate how many pounds of garden lime you need to raise lawn soil pH based on area, current pH, target pH, and soil type.
How to use this tool
- Get a soil test to find your current pH (kits available at garden centres).
- Enter current pH, target pH, and soil type.
- Enter your lawn area in square feet.
- The calculator returns pounds of ground limestone to apply.
Calculate how much lime to apply to correct your lawn's soil pH for healthy grass growth.
Formula
Lime needed (lbs) = (Area ÷ 1000) × (Target pH − Current pH) × Soil Factor
Where Soil Factor is: sandy = 40, loam = 60, clay = 100 lbs per 1,000 ft² per pH unit. Result is rounded to the nearest whole pound; negative values return 0.
How it works
This calculator estimates the pounds of ground agricultural limestone needed to raise lawn soil pH, using a standard soil-buffer factor that varies by texture: sandy soils have low buffering capacity and need less lime per pH unit, while clay soils bind more tightly and require more. The formula scales linearly with lawn area and pH deficit.
Rates assume pelletized or finely ground calcitic limestone (calcium carbonate) applied once per season. Actual requirements can vary with organic matter content, existing calcium levels, and lime particle size; a laboratory soil test with a buffer-pH reading gives the most precise prescription.
Worked example
Worked example
- Lawn area: 1,000 ft². Current pH: 6.0. Target pH: 6.5. Soil type: loam (factor = 60).
- pH difference = 6.5 − 6.0 = 0.5 pH units.
- Lime = (1000 ÷ 1000) × 0.5 × 60 = 1 × 0.5 × 60 = 30 lbs.
- Round to nearest whole pound: 30 lbs.
Lime needed: 30 lbs
Key terms
- Soil pH
- A logarithmic measure of soil acidity or alkalinity on a 0–14 scale; most lawn grasses grow best between pH 6.0 and 7.0.
- Agricultural lime
- Ground calcium carbonate (calcite) or calcium-magnesium carbonate (dolomite) applied to neutralize soil acidity and supply calcium.
- Soil buffer capacity
- A soil's resistance to pH change; clay and organic matter hold more hydrogen ions, so more lime is needed to shift pH in fine-textured soils.
- Loam
- A balanced soil texture with roughly equal proportions of sand, silt, and clay, offering moderate buffering and good drainage.
- pH unit
- Each pH unit represents a tenfold difference in hydrogen-ion concentration; moving from pH 5.5 to 6.5 requires substantially more lime than a half-unit shift.
Frequently asked questions
- How much lime do I need to raise soil pH?
- The amount depends on soil type and the desired pH change. Sandy soils need less lime (≈40 lbs per 0.5 pH unit per 1,000 ft²); clay soils need more (≈50 lbs). Always confirm with a soil test.
- How often should I lime my lawn?
- Test your soil every 2–3 years. Most lawns in humid climates need liming every 2–3 years to maintain a pH of 6.0–7.0. Apply lime in fall for spring availability.