This free lawn soil test calculator turns the numbers on your soil report into a simple lime and fertilizer plan. Enter the pH, phosphorus and potassium from your soil test report, plus your grass type, soil texture and lawn size. You get how much lime or sulfur to spread (split into safe applications), whether you need phosphate or potash, and a nitrogen plan in pounds of product for the fertilizer you actually buy.
How to use the Lawn Soil Test Calculator
- Choose your grass type and soil texture, and enter your lawn area.
- Enter the soil pH and target pH from your report.
- Enter phosphorus (P) and potassium (K) as Mehlich-3 values.
- Pick the fertilizer you plan to use and its bag size, then press Get my lawn plan.
Rates from the lawn soil test calculator are given per 1,000 sq ft, the unit most soil labs use for turf. For how labs sample and analyse soil, see Wikipedia’s overview of the soil test.
How this lawn soil calculator works
Lime and sulfur: the amount needed to change pH depends on your soil’s buffering capacity, which rises with clay and organic matter. The calculator uses typical extension rates per 1,000 sq ft for each full pH unit:
| Soil texture | Limestone to raise pH 1 unit | Sulfur to lower pH 1 unit |
|---|---|---|
| Sand / loamy sand | 25 lb | 8 lb |
| Sandy loam | 40 lb | 10 lb |
| Loam | 55 lb | 13 lb |
| Silt loam | 70 lb | 15 lb |
| Clay loam / clay | 80 lb | 18 lb |
If your report gives a buffer pH or a specific lime recommendation, use the lab’s figure. It measures your soil’s actual buffering and is more accurate than a texture-based estimate.
Ideal soil pH by grass type
- Kentucky bluegrass, ryegrass, tall fescue, St. Augustine: pH 6.0–7.0 (target 6.5)
- Fine fescue, bermuda, zoysia: pH 5.8–6.8
- Centipedegrass: pH 5.0–6.0. Do not lime centipede lawns above 6.0.
Phosphorus and potassium ratings (Mehlich-3)
Rating bands differ slightly between labs and states. This tool uses: P < 10 ppm very low, 10–25 low, 26–50 medium, > 50 high; K < 50 ppm very low, 50–100 low, 101–175 medium, > 175 high. If your report gives its own rating (low, medium, optimum), trust that.
Frequently asked questions
How much lime do I need per 1,000 square feet?
Typically 25–80 lb of limestone per 1,000 sq ft for each full unit of pH increase, depending on soil texture. Sandy soils need the least and clay soils the most. Never apply more than about 50 lb per 1,000 sq ft in one go.
Can I apply lime and fertilizer at the same time?
Yes. Lime can be spread with most fertilizers. The exception is fertilizers containing ammonium-N on high-pH soils, which can lose nitrogen as ammonia. Spread them a week or two apart if you are unsure.
How long does lime take to change soil pH?
Pelletized or finely ground lime starts working within weeks, but the full effect takes 3–6 months or longer. Retest about a year after applying.
My lab reports potassium in lb/acre. How do I convert?
For a standard 6-inch sample depth, lb/acre ÷ 2 ≈ ppm. So 200 lb/acre ≈ 100 ppm.
How do I read soil test results?
Look at pH first, then phosphorus and potassium. Most labs rate P and K as low, medium (optimum) or high, and only low or medium results need fertilizer. Check the extraction method (usually Mehlich-3) and the unit: lb/acre is roughly ppm × 2.
What is the best soil pH for grass?
Most lawn grasses grow best between pH 6.0 and 7.0. Centipedegrass prefers about 5.0 to 6.0, so it rarely needs lime. Below the target range add lime; well above 7.0, elemental sulfur lowers pH slowly.
Related tools
General guidance based on typical US extension recommendations. Follow your soil lab’s specific recommendations, product labels and local fertilizer regulations. Built by a soil and fertilizer testing laboratory professional.