Pasture Rotation Calculator
Calculate the sustainable carrying capacity of your rotational grazing system based on paddock count, grass growth, and livestock units. Use it to design a rotation schedule that prevents overgrazing and maintains pasture health.
About this calculator
Rotational grazing divides total pasture into paddocks that rest and regrow while livestock graze others in sequence. The key output is a carrying-capacity index comparing pasture productivity to animal demand. The formula is: Index = (totalPasture / numberOfPaddocks) × grassGrowthRate / (animalUnits × (grazingDays + restPeriod) / 30). The first factor gives the average size of each paddock. Multiplying by grassGrowthRate expresses how much forage each paddock produces in relative terms. The denominator converts animal units and the total rotation cycle length (grazing days plus rest period) into a monthly demand figure. A result above 1 suggests the system can sustain the current herd; below 1 signals overgrazing risk. Adjusting paddock count, rest period length, or stocking density directly shifts this index, making the calculator a practical design tool for new and existing rotational systems.
How to use
Example: 200-acre farm, 8 paddocks, 50 animal units, grass growth rate 1.2, 7 grazing days per paddock, 28-day rest period. Step 1 — Paddock size: 200 / 8 = 25 acres. Step 2 — Numerator: 25 × 1.2 = 30. Step 3 — Denominator: 50 × (7 + 28) / 30 = 50 × 35 / 30 = 58.33. Step 4 — Index: 30 / 58.33 ≈ 0.51. This result below 1 indicates the current stocking rate may exceed sustainable capacity — consider reducing animal units or adding paddocks.
Frequently asked questions
How do I determine the correct rest period length for rotational grazing?
Rest period is the time a paddock is left ungrazed to allow grass to recover to its target pre-grazing height, typically 8–12 inches for cool-season grasses. In spring, rapid growth means rest periods can be as short as 18–21 days; in midsummer heat or drought, 45–60 days may be needed. Monitoring actual plant height before re-entry is more reliable than a fixed calendar schedule. The rest period entered in this calculator directly affects the rotation cycle length and therefore the estimated carrying capacity — longer rest periods increase total cycle time and reduce the effective stocking rate the system can sustain.
What is an animal unit and how do I calculate it for mixed livestock herds?
An animal unit (AU) is a standardized measure of forage consumption, defined as one 1,000-pound beef cow with or without a calf consuming approximately 26 pounds of dry matter per day. Other livestock are converted using coefficients: a mature horse ≈ 1.25 AU, a sheep or goat ≈ 0.2 AU, and a stocker calf ≈ 0.5 AU. To calculate total AU for a mixed herd, multiply the count of each species by its coefficient and sum the results. Accurate AU input is critical because the denominator of the rotation formula scales directly with stocking density.
Why is splitting pasture into more paddocks better for grass recovery?
More paddocks mean each individual paddock is grazed for fewer days before the herd moves on, giving grass a longer, uninterrupted rest period to rebuild root reserves and leaf area. Research consistently shows that pastures grazed with adequate rest periods produce 20–40% more total forage annually than continuously grazed equivalents. In this calculator, increasing numberOfPaddocks reduces the per-paddock grazing pressure in the numerator, which typically raises the carrying-capacity index toward or above 1. The practical minimum is usually four paddocks, but eight to twelve paddocks are common in well-designed systems.