What is an Animal Unit (AU)?

One Animal Unit is a 1000 lb beef cow with calf, defined to consume about 26 lb of dry matter per day, roughly 780 lb per month. Other animals are scaled by an Animal Unit Equivalent: a 1000 lb dry cow is about 0.92 AU and a mature ewe is about 0.20 AU.

Why apply a utilisation percentage instead of 100 percent?

Grazing all the forage destroys plant regrowth, roots, and ground cover. The take-half-leave-half rule and stricter range guidance cap safe harvest at roughly 25 to 50 percent so the pasture recovers. The remainder protects the stand and soil.

How is the stocking rate calculated?

Total dry matter is area times yield. Multiply by utilisation to get usable forage, divide by daily intake (26 lb per AU) to get animal-unit grazing days, then divide by your planned days to get the number of animal units the pasture can carry.

What is an AUM and how does it relate?

An Animal Unit Month (AUM) is the forage one animal unit eats in a month, about 780 lb of dry matter. Dividing usable forage by 780 gives the AUMs a pasture provides, a common unit for leasing and public-land grazing fees.

Where do I get a forage yield estimate?

Clip and weigh a known area, dry it, and scale to per-acre, or use NRCS ecological site descriptions and extension production tables for your region and rainfall year. Yield varies enormously by soil, species, and season, so update it each year.

Livestock Stocking Rate Calculator

Overstocking a pasture is the fastest way to degrade it, while understocking wastes grass and money. This calculator turns acres and a forage-yield estimate into Animal Unit Equivalents and a safe stocking rate, applying a utilisation cap so you graze sustainably and can plan rotation timing.

How it works

The chain from forage to animals runs through the Animal Unit standard, where one AU eats about 26 lb of dry matter per day (about 780 lb per month):

total DM (lb)   = area (ac) × yield (lb DM/ac)
usable DM (lb)  = total DM × (utilisation % / 100)
AU-days         = usable DM / 26
AUMs            = usable DM / 780
animal units    = AU-days / planned grazing days

Multiply the resulting animal units by your herd’s AUE per head to get the actual number of cows, steers, or ewes the pasture can safely carry for the period.

Example and tips

A 120-acre pasture yielding 2,000 lb DM/acre at 30 percent utilisation provides 120 x 2,000 x 0.30 = 72,000 lb of usable forage, about 92 AUMs. Grazed over 120 days that supports roughly 23 animal units; at an AUE of 0.92 for dry cows that is about 25 head. Re-clip and re-estimate yield every year, since a drought year can cut production in half and your safe stocking rate with it.