Lime Calculator: How Much Lime to Raise Soil pH
Enter your current and target soil pH, the buffer capacity of your soil, the calcium carbonate equivalent (CCE) printed on the lime and the area and depth you will work it into. This is an estimate using typical values; a soil test with a lime recommendation is more reliable.
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Formula
- pH change = target pH - current pH
- Pure calcium carbonate needed = buffer capacity x pH change x (depth / reference depth) x area
- Lime product needed = pure calcium carbonate / (CCE / 100)
Reference depth is 6 in (imperial, buffer in short tons per acre) or 15 cm (metric, buffer in tonnes per hectare). 1 acre = 43,560 sq ft, 1 short ton = 2,000 lb, 1 ha = 10,000 m2.
Worked example
Raise pH from 5.5 to 6.5 on 1,000 sq ft, worked in to 6 in, with a buffer capacity of 2 tons per acre per pH unit and lime with a CCE of 90:
- Pure calcium carbonate = 2 x 2,000 lb x (1,000 / 43,560) x 1 x (6 / 6) = 91.83 lb
- Lime product = 91.83 / 0.90 = 102.03 lb, about 102 lb per 1,000 sq ft
Metric check: 1 ha, 2 t/ha per pH unit, pH 5.0 to 6.5, 15 cm, CCE 100 gives 2,000 x 1.5 = 3,000 kg, or 0.3 kg per m2.
When to use it
Use it after a soil test shows acidic soil, to turn a pH goal into a quantity of lime to buy. Buffer capacity depends on the soil: sandy soils have a low value and heavy clay or organic soils a higher one.
Common mistakes
- Guessing the buffer capacity. Use the value from your soil test where you can.
- Ignoring the depth. Working lime into 3 inches needs half as much as 6 inches.
- Forgetting CCE. A weaker product needs a proportionally larger amount.
How it differs from nearby calculators
The pH calculator is a chemistry tool for the pH of a solution, not for soil. This page sizes a lime product for a lawn or bed, and the fertilizer NPK calculator sizes nutrient products instead.
Frequently asked questions
How much lime do I need to raise soil pH by one point?
It depends on how strongly your soil resists change (its buffer capacity). As a typical figure, a loam might need about 2 tons of pure lime per acre for 1 pH unit in the top 6 inches. For 1,000 sq ft that is 2 x 2,000 x 1,000 / 43,560 = 91.8 lb of pure lime, and about 102 lb of a product with a CCE of 90. A soil test gives a figure for your own soil.
What is calcium carbonate equivalent (CCE)?
CCE rates how well a liming product neutralises acid compared with pure calcium carbonate, which is 100. A product with CCE 80 is only 80 percent as strong, so you need 100 / 80 = 1.25 times as much. Check the bag or supplier data; typical ground limestone is roughly 90 to 100, while some products are higher or lower.
Why does soil type change the amount of lime?
Clay and organic soils hold more acidity in reserve than sandy soils, so they need more lime to move the same pH. The buffer capacity input stands in for that. Typical values run from about 0.5 to 1 ton per acre per pH unit for sand up to about 2 to 3 for heavy clay, but your soil may differ, so use a soil test where you can.
How deep does the lime need to go, and should I add it all at once?
The estimate assumes the lime is mixed through the depth you enter, scaling the amount from a 6 inch (15 cm) reference layer. Working it into 3 inches instead of 6 needs half as much. Lime moves slowly, so large amounts are often split into two applications, and the pH should be retested after a few months. Take a soil test before liming, since overliming can raise pH too far.
How much lime to raise soil pH from 5.5 to 6.5 on 1,000 square feet?
With the default buffer capacity of 1.5 tons per acre per pH unit, a 6 inch depth and a CCE of 90, the pure lime is 68.87 lb. Dividing by 0.90 gives about 76.5 lb of product. A soil test tells you the right buffer capacity.
How much lime for 10,000 square feet with a buffer capacity of 2?
Use the same pH change and depth: 2 x 2,000 x (10,000 / 43,560) = 918.3 lb of pure lime. A product with CCE 90 then needs about 1,020 lb, or 102 lb per 1,000 sq ft.
How many kilograms of lime per square metre?
In metric units, 2 tonnes per hectare per pH unit and a rise of 1.5 units over 15 cm needs 3,000 kg of pure lime per hectare. On 100 m2 that is 30 kg in total, or 0.3 kg per m2 at a CCE of 100.