Soil pH Amendment Calculator

Soil pH Amendment Calculator

Most vegetables and garden plants prefer a soil pH somewhere in the 6.0-7.0 range - this calculator estimates how much lime (to raise pH) or elemental sulfur (to lower pH) you need to reach your target.

Amendment Needed = (Area / 100 sq ft) x pH Difference x Rate Per 100 sq ft Per pH Unit

Example

Raising soil from pH 5.5 to 6.5 across 200 sq ft:

pH Difference = 1.0 → 10 lbs of garden lime

Lime vs. Sulfur

Garden lime raises soil pH (reduces acidity), while elemental sulfur lowers it (increases acidity) - the two amendments work through entirely different chemical mechanisms and are not interchangeable, so make sure you're applying the correct one for the direction you actually need to shift.

Soil Type Changes the Math

These reference rates assume average loam soil - sandy soils generally need less amendment to shift pH by the same amount (since sand has low buffering capacity), while clay soils need considerably more, since clay's higher buffering capacity resists pH change more strongly. Soil pH also shifts gradually over weeks to months after amendment, so retesting before applying more is strongly recommended rather than adding a large single dose all at once.