Soil Amendment Calculator
Calculate how much agricultural lime and organic matter you need — and what it will cost — to bring your soil to its target pH and fertility level. Use it after receiving a soil test report before planting season.
Last updated: September 2026
Formula below · 2 sources (usda.gov, Wikipedia) · Updated Sep 2026
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About this calculator
Raising soil pH requires lime, and the amount needed depends on how far your current pH is from the target, your soil's buffering capacity (represented by soil type), and field size. The calculator uses a baseline of 2,000 lb (1 ton) of agricultural lime per acre per pH unit, scaled by a soil factor of 0.8 for sandy soil, 0.9 for sandy loam, 1.0 for loam and 1.3 for clay — that is 1,600 to 2,600 lb per acre per pH unit. Lime cost = fieldSize × max(0, targetPH − currentPH) × soilFactor × 1 ton × limeCost ($/ton). The second term adds organic matter (compost or manure) at a flat $45 per ton: fieldSize × organicMatter (tons/acre) × 45. Total Cost = fieldSize × max(0, targetPH − currentPH) × soilFactor × limeCost + fieldSize × organicMatter × 45. The max(0, …) guard prevents negative lime quantities when soil is already at or above the target pH. Sandy soils require less lime per pH unit than heavy clay soils because they have lower cation exchange capacity and weaker buffering. Your soil test's buffer pH gives a more precise lime rate; if your lime's CCE is below 100%, divide the tonnage by CCE/100.
How to use
Scenario: 10-acre field, current pH 5.8, target pH 6.5, sandy soil (factor 0.8), organic matter addition 0.5 tons/acre, lime costs $35/ton. Step 1 — pH gap: 6.5 − 5.8 = 0.7. Step 2 — Lime: 0.7 × 0.8 = 0.56 tons/acre, or 5.6 tons for the field. Step 3 — Lime cost: 5.6 × $35 = $196. Step 4 — Organic matter: 10 × 0.5 × $45 = $225. Total = $196 + $225 = $421 ($42.10 per acre). Enter your tested values to generate a site-specific amendment budget.
Frequently asked questions
How much lime does it take to raise soil pH by one unit?
The lime requirement per pH unit varies widely by soil texture and organic matter content. Sandy soils with low buffering capacity may need only 1,000–1,500 lb of agricultural lime per acre per pH unit, while heavy clay soils can require 3,000–4,000 lb for the same shift. This calculator uses 2,000 lb as a baseline, scaled by the soil-type factor (0.8 to 1.3) you select. Always cross-reference with your state's lime requirement tables or an extension lab recommendation for the most accurate application rate.
What is the difference between agricultural lime and dolomitic lime for soil amendment?
Agricultural lime (calcitic lime) is primarily calcium carbonate (CaCO₃) and raises pH while supplying calcium. Dolomitic lime contains both calcium carbonate and magnesium carbonate, making it preferable when soils are also magnesium-deficient. The neutralizing value of dolomitic lime is slightly different, so application rates may need minor adjustment. Your soil test will indicate magnesium levels; if they are low, choosing dolomitic lime addresses two deficiencies in one amendment pass and can be more cost-effective.
When is the best time to apply lime and organic matter amendments to a field?
Fall application is generally preferred for lime because it gives the material three to six months to react with soil moisture and begin raising pH before spring planting. Organic matter such as compost or manure can be applied in fall or early spring, though fall incorporation allows winter microbial activity to begin breaking down material. Avoid applying lime and fresh manure simultaneously, as the alkaline conditions can cause nitrogen volatilization losses. Splitting large lime applications across two seasons is advisable when the required rate exceeds two tons per acre.