About the Garden Lime Calculator
This garden lime calculator estimates how much lime to apply to raise the pH of acidic soil. Enter your current soil pH, the target pH for what you grow (6.0–7.0 suits most lawns and vegetables), the soil texture and the area, and it returns the pounds of product to spread, the rate per 1,000 square feet, the number of bags and how many separate applications to split it into.
It is for homeowners and gardeners who have a pH reading from a home test kit or a soil lab and want a sensible ballpark. Clay and organic soils hold more acidity in reserve than sandy soils, so they need much more lime to move the pH by the same amount; that is why soil texture is the biggest input here.
Rates are rule-of-thumb estimates for finely ground limestone working into the top 6–7 inches of soil. A lab soil test that reports buffer pH or a lime requirement is more accurate and should override this estimate. Lime cannot lower pH — for alkaline soil you need elemental sulfur instead.
With the default inputs, the lime to apply is 140 lb. Change any value above to recalculate instantly.
How to use the garden lime calculator
- 1Test your soil pH with a kit or a lab test.
- 2Enter the current pH and the target pH for your plants.
- 3Choose your soil texture and enter the area in square feet.
- 4Pick the lime product (or enter the CCE from the bag label).
- 5Spread the amount with a drop or broadcast spreader, splitting large doses, and water it in.
Formula and method
The soil factor is the approximate pounds of finely ground limestone needed per 1,000 square feet to raise the pH of the top 6–7 inches by one unit: about 25 lb for sand, 50 for sandy loam, 70 for loam, 95 for silt loam, 120 for clay and 200 for organic soils. These are rounded rule-of-thumb values in line with classic extension texture tables; heavier and more organic soils have more reserve acidity to neutralize.
Products are scaled by their calcium carbonate equivalent (CCE): pure limestone is 100%, so hydrated lime at about 135% needs roughly three-quarters as much. Because large surface applications can cake on the soil, NC State Extension recommends no more than 50 lb per 1,000 sq ft at a time, so bigger amounts are split.
- Soil factor
- lb limestone per 1,000 sq ft per pH unit for the soil texture
- CCE
- Calcium carbonate equivalent of the product, %
- Area
- Area to treat in square feet
Worked examples
Loam lawn, pH 5.5 to 6.5, 2,000 sq ft
Raising loam soil by one pH unit takes about 70 lb of limestone per 1,000 sq ft, so 2,000 sq ft needs 140 lb — four 40 lb bags. Because 70 lb is above the 50 lb per application guideline, it is split into two applications.
Sandy vegetable bed, pH 5.8 to 6.5, hydrated lime
A 0.7 pH rise on sand needs 0.7 × 25 = 17.5 lb of limestone per 1,000 sq ft. Hydrated lime is about 135% as strong, so 17.5 ÷ 1.35 ≈ 13 lb per 1,000 sq ft — about 6.5 lb for 500 sq ft.
Clay garden, pH 5.0 to 6.5, custom product 90% CCE
A 1.5 unit rise on clay needs 1.5 × 120 = 180 lb of pure limestone per 1,000 sq ft, and at 90% CCE that is 180 ÷ 0.9 = 200 lb. At 50 lb per application this should be spread over four applications.
Frequently asked questions
How much lime do I need per 1,000 square feet?+
To raise pH by about one unit, rough rates are 25 lb of ground limestone per 1,000 sq ft on sand, 50–70 lb on sandy loam and loam, and 100–120 lb on clay. A lab soil test with a lime recommendation is the most accurate guide.
How much lime can I apply at once?+
NC State Extension advises applying up to 50 lb of lime per 1,000 sq ft in one surface application on established lawns, gardens and ornamentals, and waiting several months before repeating for larger recommendations.
How long does lime take to raise soil pH?+
Finely ground limestone starts working within weeks but takes 3–6 months or more to fully react, faster if it is tilled in and the soil is moist. Pelletized lime is ground limestone bound into pellets and reacts at a similar speed.
Should I use dolomitic or calcitic lime?+
Both raise pH similarly. Dolomitic lime also supplies magnesium, so it is the better choice when a soil test shows low magnesium; calcitic lime is preferred when magnesium is already adequate or high.
When is the best time to lime a lawn?+
Fall and early spring are ideal because rain and freeze-thaw cycles help work the lime into the soil. Avoid liming at the same time as applying ammonium-based nitrogen fertilizer.