Tool
Stocking rate calculator (animal units per acre and AUMs)
Calculate nowQuick answer
Multiply head count by average weight and divide by 1,000 lb to get animal units (AU). Divide AU by acres for stocking rate. For carrying capacity, multiply forage dry matter per acre by acres and by harvest efficiency (about 25% under take-half-leave-half), then divide by 25 lb per AU per day times grazing days. University of Wyoming Extension defines one AUM as 750 lb of dry forage.
How the math works
- AU = head × average weight ÷ 1,000 lb.
- Stocking rate = AU ÷ acres (and acres per AU is the inverse).
- Carrying capacity (optional) = lb DM/acre × acres × harvest efficiency ÷ (25 lb/AU/day × grazing days). Multiply AU by months grazed to get AUMs.
Source and limits
Definitions and defaults come from Animal Unit Month (AUM) Concepts and Applications for Grazing Rangelands, University of Wyoming Extension B-1320. Lactating cows and growing cattle eat differently from their weight alone; adjust forage per AU when you know your herd’s intake.
Frequently asked questions
What is an animal unit?
A 1,000-lb cow, with her unweaned calf in the AUM definition. A 1,300-lb cow counts as about 1.3 AU when you scale by weight.
How much forage is one AUM?
University of Wyoming Extension uses 750 lb of dry forage: a 1,000-lb cow eating 2.5% of body weight a day for 30 days. Some agencies use other values, so agree on the number in a lease.
Why only 25% harvest efficiency?
Under take-half-leave-half, half the forage stays for regrowth and about half of the rest is lost to trampling, wildlife and waste. Irrigated pasture or dormant-season grazing can allow more.
Sources
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