How this calculator works
This tool estimates available dry matter (DM) from pasture area, forage production, and a utilization percentage, then divides by herd intake to compute grazing days or head capacity. It also converts total DM to AUMs (Animal Unit Months).
Formulas
- Available forage (lb) = acres × forage (lb/ac) × utilization%
- Daily intake/head (lb) = body weight × intake%
- Grazing days = available forage ÷ (head × intake/head/day)
- Head capacity = available forage ÷ (days × intake/head/day)
- AUMs = available forage ÷ 780 (lb DM per AUM)
Assumptions & notes
- Use dry matter forage values for consistency across seasons and species.
- Utilization reflects trampling, fouling, regrowth needs, and residuals left behind.
- Typical intake for beef cattle on pasture is ~2.5% BW/day; growing animals may be higher.
- Be conservative if you lack records; overshooting utilization can harm stand vigor.
Worked example
40 ac, 2,500 lb/ac forage, 40% utilization, 1,200 lb cattle @ 2.5% intake, 35 head:
- Available forage = 40 × 2,500 × 0.40 = 40,000 lb
- Intake/head/day = 1,200 × 0.025 = 30 lb
- Grazing days = 40,000 ÷ (35 × 30) ≈ 38 days
- AUMs = 40,000 ÷ 780 ≈ 51.3 AUM
FAQ
What intake rate should I use? 2.5% BW/day is a common planning value for beef cattle; sheep/goats often 3–4%.
What utilization percent should I use? 25–35% continuous; 40–60% rotational (varies by season/species—use your records).
How are AUMs calculated? 1 AUM ≈ 780 lb DM (26 lb/day × 30 days).
Can I switch to metric? Yes—use the toggle above. Inputs/labels convert between acres/hectares, lb/kg, and lb/ac ↔ kg/ha.
Prepared by AgCalculator · Last updated November 3, 2025