Lawn lime calculator

Lime rates come from a soil test, usually as pounds of ground limestone per 1,000 sq ft. If your report only gives pH and a buffer pH, the calculator works the rate out with Ohio State’s buffer-pH equations. Then it adjusts for your product’s calcium carbonate equivalent (CCE) — the percentage printed on the bag that says how strongly it neutralizes acidity compared with pure ground limestone (100%) — and on an established lawn splits big doses: 50 lb per 1,000 sq ft at a time is a common limit.

How the lime calculation works

Soil labs report a lime requirement as an amount of pure ground limestone (calcium carbonate, CCE 100%) per area. Real products neutralize acidity a little more or less than that, which the label states as the calcium carbonate equivalent. Penn State Extension’s formula is the recommendation ÷ CCE × 100: a 75 lb recommendation with an 80% CCE product becomes about 94 lb. Then multiply by your area.

product per 1,000 sq ft = soil-test rate ÷ (CCE ÷ 100)
total = that × lawn area ÷ 1,000
applications = product per 1,000 sq ft ÷ max per application (round up)
1 ton per acre ≈ 46 lb per 1,000 sq ft

No lime rate on your report? Use the buffer pH

Soil pH tells you the soil is acidic; it does not tell you how much lime it takes to fix it, because clay and organic soils hold far more reserve acidity than sandy ones. That is what the buffer pH measures. Ohio State University Extension’s fact sheet AGF-505 turns the SMP buffer pH into a lime requirement in tons per acre, for liming material with an effective neutralizing power (ENP) of 2,000 lb per ton mixed 8 in deep:

target pH 6.8: tons/acre = 46.8098 − 6.7553 × buffer pH
target pH 6.5: tons/acre = 39.1496 − 5.6399 × buffer pH
target pH 6.0: tons/acre = 31.7602 − 4.5721 × buffer pH
lb per 1,000 sq ft = tons/acre × 45.9
other depths: × depth ÷ 8 in

Pick pH 6.5 as the target unless your report names another: NDSU Extension calls 6.5 ideal for most turfgrasses. Surface-applied lime on an established lawn only reaches the top few inches, so the calculator uses 4 in — half the equation’s rate, which is also how AGF-505 handles no-till fields. For a new lawn it uses the depth you till to. If the soil pH is already at or above your target, it returns no lime whatever the buffer pH says. Example: buffer pH 6.6 with a 6.5 target gives 1.93 tons per acre, about 88 lb per 1,000 sq ft tilled 8 in deep, or about 44 lb spread on an established lawn.

CCE, ENP and pelletized lime

CCE measures only the chemistry: how much acid a pound of the material can neutralize compared with pure calcium carbonate. Ohio labels and AGF-505 use ENP instead, which also counts fineness (coarse chips react slowly) and moisture; 2,000 lb per ton is the 100% reference, so divide ENP by 20 to enter it here. Pelletized lime is finely ground limestone pressed into pellets with a binder so it spreads cleanly — AGF-505 lists it at 1,860 lb ENP per ton, or 93%. The pellets break down with the first good rain or watering.

How much lime at once?

Lime spread on top of an established lawn moves into the soil slowly, and very heavy single doses can sit on the surface. Ohio State University Extension caps ground, dolomitic and pelletized limestone at 50 lb per 1,000 sq ft per application and splits anything larger into two applications during the year; Purdue’s sod guide uses the same 50 lb limit, while Penn State Extension allows up to 100 lb on established turf. When building a new lawn, Penn State notes the whole requirement can go down at once if it is mixed into the top 4–6 in of soil before seeding or sodding.

Tips

• Test first. Lime fixes low pH. Many lawns don’t need it, and over-liming causes its own nutrient problems. If the pH is too high, the fix is sulfur, not lime — see the soil sulfur calculator.
• Calcitic or dolomitic? Dolomitic lime also supplies magnesium; use it if your soil test shows low magnesium.
• Pelletized vs powdered: the same material, but pellets spread cleanly with an ordinary lawn spreader.
• Spring and fall are the usual windows; avoid spreading on frozen ground or right before heavy rain.

Fertilizing the same lawn? Once pH is sorted, the nitrogen math is next: see how much 24-0-6 fertilizer for 5,000 sq ft, or, for a balanced product, how much 10-10-10 fertilizer per 1,000 sq ft.

CCE and buffer pH are defined in plain English in words you’ll hear at the yard.