Lime Application Calculator (Raise Soil pH)

How it works

kg CaCO₃ = (rate per pH unit per 100 m²: sand 20, loam 35, clay 50, peat 70) × pH rise × area ÷ 100; actual lime = ÷ calcium carbonate equivalent (CCE)

Lime neutralises soil acidity, but how much you need depends less on the pH gap than on the soil’s buffering capacity — clay and organic matter hold far more exchangeable acidity than sand, so raising a clay soil by one unit takes two to three times the lime a sandy soil needs. The figures here are typical extension-service rates for the top 15 cm; a laboratory buffer-pH or lime-requirement test is more accurate. Lime types differ in neutralising power: dolomite is slightly stronger and adds magnesium, hydrated lime is fast but caustic and easy to overdo, wood ash is weak and variable. Apply in stages, never more than about 50 kg of carbonate per 100 m² at once, and re-test before repeating — over-liming locks up iron, manganese and phosphorus and is harder to reverse than acidity.

Worked example

50 m² of loam from pH 5.4 to 6.5: 35 × 1.1 × 0.5 = 19.3 kg of garden lime — about 385 g/m², one 25 kg bag with some to spare.

Frequently asked questions