Estimate usable manure storage (gallons and days) from pit/lagoon inside dimensions, freeboard, and daily manure plus washwater.
Use this for first-pass sizing of a rectangular pit or tank, or to check whether existing storage covers your required winter/storage days.
Subtract freeboard and sludge depth from total depth before counting usable volume. Sloped lagoons need a stage-storage curve — this page is a rectangular estimate.
Usable depth = total − freeboard/sludge. Gallons = L × W × usable_depth × 7.48. Days = usable gallons ÷ daily inflow.
usable_ft = depth − freeboard_sludge
gal = L × W × usable_ft × 7.48
days = gal ÷ gal_per_day
Include washwater, bedding liquids, and rainfall/runoff in daily volume when your plan requires it.
Pit 80 × 40 × 10 ft with 2 ft freeboard/sludge → 8 ft usable → 25,600 ft³ × 7.48 ≈ 191,500 gal. At 5,000 gal/day → about 38 days (short of a 180-day winter target).
Assumptions: vertical walls; uniform usable depth; daily volume is steady.
Limits: not an NRCS design or permit document; sloped lagoons and treatment volumes need engineer tables.
Responsibility: follow state waste-storage rules and a qualified designer for construction.
Empty depth kept for rainfall, waves, and safety — plus sludge that permanently occupies the bottom.
This page is for liquid/slurry volume. Stacking sheds use tons and pad area instead.
Add average precipitation × surface acres to daily or seasonal inflow when required by your plan.