Cattle per Acre Calculator (stocking rate from forage yield & AUM)

Understanding the cattle per acre (stocking rate) calculator — concept and principle

How many cattle can a pasture support for a grazing season? This calculator estimates the stocking rate from forage production, the share you plan to graze and the animals' forage demand, using animal units (AU) and animal unit months (AUM).

Half of 2,000 lb per acre is 1,000 lb usable, 1.25 AUMs; over 160 acres that feeds 40 pairs for five months.

How it is calculated

One animal unit (AU) is a 1,000-lb cow with her calf, eating about 26 lb of forage dry matter a day; one AUM ≈ 800 lb of dry matter.
Usable forage = yield × share grazed.
AUMs per acre = usable forage ÷ 800 lb.
Animals = total AUMs ÷ (grazing months × AU equivalent), rounded down.
Other animals are scaled by their AU equivalent or by (weight ÷ 1,000 lb)^0.75. Metric inputs: 1 kg/ha = 0.892 lb/acre.

The principle

Stocking rate balances supply and demand. A pasture produces a certain amount of forage in a season, but not all of it should be eaten: leaving a share protects plant regrowth, soil and wildlife habitat. A common guideline is "take half, leave half". Dividing the usable forage by what one animal eats per month gives how many animal-months the pasture can support.

Worked example

Default inputs: 2,000 lb dry matter per acre, 50% grazed, 5 months, cow with calf (1.0 AU), 160 acres.

Usable forage = 2,000 × 0.50 = 1,000 lb per acre.
AUMs per acre = 1,000 ÷ 800 = 1.25.
Total AUMs = 1.25 × 160 = 200.
Animals = 200 ÷ (5 × 1.0) = 40 cow–calf pairs.
Area per animal = 160 ÷ 40 = 4 acres (about 1.62 ha); AU equivalent = 1.

Each point is the calculator re-run with only “Grazing period (months)” changed; the gold point is the default example. Change the inputs above and this chart follows your numbers.

Grazing period (months)	Animals the pasture can carry
1.25	160
2.5	80
3.75	53
5	40
6.25	32
7.5	26
10	20

How to read the result

Start conservatively and adjust with monitoring of forage height and animal condition. Drought years can cut forage production sharply, so plan destocking triggers in advance. Larger cows or animals with high demands (lactating, growing) have AU equivalents above 1.

Common mistakes

Using total forage instead of the share safely grazed.
Using wet (as-fed) weight instead of dry matter.
Forgetting that a cow with calf counts as one AU, not two.
Assuming the same yield every year.

Keep in mind: Stocking rates must reflect local conditions. Consult local extension services or range specialists before setting rates.

Frequently asked questions

How many cows per acre?

It depends on forage production; in the default example, 4 acres per cow–calf pair for a 5-month season.

What is an AUM?

The forage one animal unit eats in a month, about 800 lb of dry matter.

Why only graze 50%?

Leaving forage protects regrowth, soil and future production.

Sources: Society for Range Management, A Glossary of Terms Used in Range Management (animal unit, AUM) · USDA NRCS, National Range and Pasture Handbook

Checked 9 Nov 2026. Alberta Agriculture and Forestry, “Using the Animal Unit Month (AUM) Effectively”, Agdex 420/16-1, revised March 2017: 1 AU = 1,000-lb cow with calf, about 26 lb dry matter per day (2.6% of body weight), 1 AUM ≈ 800 lb dry matter; AU equivalents bull 1.3, yearling 0.67, weaned calf 0.5; weight-based equivalents (weight/1,000 lb)^0.75; leave 50–60% of the year’s growth.

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