Lime Requirement Calculator & Raise Your Soil pH
Sizes lime for acidic loam
Find how much agricultural lime to apply to raise your soil from its current pH to a target — adjusted for texture, depth and the material's neutralising value — in t/ha, tonnes, bags and cost.
Current soil is Moderately acidic. Most crops prefer pH 6.0–7.0.
To raise loam soil from pH 5.5 to 6.5, apply about 3 t/ha of agricultural limestone (calcitic) — that's 1.21 tonnes (25 × 50 kg bags) over 1 acre. Heavier soils need more lime because they buffer pH more strongly.
Next: spread evenly and incorporate 2–3 months before sowing — lime reacts slowly. Split very high rates over two seasons, and re-test pH after 6–12 months rather than over-applying.
Estimate from texture-based buffering thumb rules; a soil-test buffer-pH (lime requirement) reading is more precise for your field.
Lime requirement — key facts
- Ideal crop pH
- 6.0–7.0 for most crops
- Loam, +1 pH (15 cm)
- ≈ 3 t/ha CaCO₃
- Sandy soil
- ≈ 1 t/ha per pH unit
- Clay soil
- ≈ 5 t/ha per pH unit
- Calcitic lime NV
- 100 (reference)
- Hydrated lime NV
- ≈ 136
- Reaction time
- 2–3 months+, slow
- Privacy
- Runs in your browser; nothing uploaded
How the lime rate is worked out
The starting point is how far you need to move the pH — the gap between your current and target readings. Each soil texture has a buffering rate (tonnes of pure CaCO₃ per hectare to lift one pH unit over a 15 cm layer), so the tool multiplies that rate by the pH gap and scales it for the depth you incorporate. Finally it divides by the material's neutralising value so a stronger material like hydrated lime gives a smaller tonnage than basic slag or wood ash.
Liming corrects acidity that otherwise locks up phosphorus, stunts roots and lets aluminium and manganese reach toxic levels. Getting to the right pH unlocks nutrients you've already paid for and improves the response to nitrogen and phosphate fertilizers — but over-liming is just as harmful, so aim for the target, incorporate well ahead of sowing, and re-test before topping up.
Hit your target pH
Enter current and target pH and get the exact lime tonnage for your texture and depth.
Compare materials
See how calcitic, dolomitic, hydrated lime or slag change the quantity via their neutralising value.
Plan the purchase
Total tonnes, 50-kg bags and cost in your currency so you can order the right amount.
Avoid over-liming
If your soil already meets the target, the tool tells you to hold off rather than push pH too high.
Frequently Asked Questions
How much lime do I need to raise soil pH?+
It depends on how far you must raise the pH, the soil texture and the lime's quality. As a guide, raising a loam by one pH unit over the top 15 cm needs roughly 3 tonnes of pure CaCO₃ per hectare; sandy soils need less (~1 t/ha) and clays more (~5 t/ha). This tool combines your current and target pH, texture, depth and material to give an exact rate.
Why does soil texture change the lime rate?+
Heavier soils have more clay and organic matter, which buffer pH — they resist change, so they need more lime to shift each pH unit. Sandy soils have little buffering and respond quickly to small amounts. The calculator carries a buffering rate for each texture from sand to clay.
What target pH should I aim for?+
Most field and vegetable crops do best at pH 6.0–7.0, where nutrients are most available. A target of 6.5 suits the majority. Acid-loving crops (blueberries, tea, potatoes for scab control) prefer lower pH, so don't lime those toward neutral.
What is neutralising value (NV)?+
Neutralising value, or calcium carbonate equivalent, rates a material's acid-neutralising power against pure limestone (NV 100). Hydrated lime (~136) and quicklime (~178) neutralise more per tonne, so you apply less; basic slag (~80) and wood ash (~50) need more. The tool adjusts the quantity for the material you choose.
Calcitic or dolomitic lime — which should I use?+
Both raise pH; dolomitic lime also supplies magnesium, so it's preferred where soils are low in Mg. If magnesium is already adequate, calcitic limestone avoids over-applying Mg, which can upset the calcium-to-magnesium balance. Choose based on a soil test.
How deep should I figure the lime in?+
Lime requirement is usually quoted for the plough layer — about 15 cm. If you incorporate deeper, you're treating more soil and need proportionally more lime; this tool scales the rate with the depth you enter. Lime moves down slowly, so thorough mixing helps.
How long before liming takes effect?+
Lime reacts slowly. Apply and incorporate 2–3 months ahead of sowing, ideally before the wettest period, and allow up to a full season for the pH to stabilise. Finely ground lime acts faster than coarse material.
Can I apply too much lime?+
Yes — over-liming pushes pH too high and locks up phosphorus and micronutrients such as iron, manganese and zinc, causing deficiencies. Split very large requirements across two seasons and re-test before topping up rather than over-applying in one go.
Is this as accurate as a soil test?+
It's a sound planning estimate from texture-based buffering. A laboratory buffer-pH (also called a lime requirement or SMP test) measures your soil's actual buffering and is more precise — use it where available, especially for large areas.
When is the best time to apply lime?+
Autumn or a few months before planting is ideal, so rainfall and time let the lime react and raise pH before the crop needs it. Incorporate into the topsoil rather than leaving it on the surface for fastest results.