If you want to know how many cows per acre can graze, this cattle per acre calculator will help you find the answer! Keep on reading to learn about Animal Unit and Animal Unit Month measures and see how the different pasture conditions influence how many cattle per acre may fit.

Do you want to ask the question another way around — How much space does a cow need? If so, you are at the right place to get the answer!

The animal unit — how many acres does a cow need?

The Animal Unit (AU) is a universal measure that helps you estimate how many cattle per acre you can graze. One AU is a 1000 lb cow with a calf of up to six months old.

Typically, a cow eats forage at a rate of around 75-80% of its mass per month. Although a calf doesn't need grass for grazing, it still consumes cow's milk, resulting in higher forage consumption by the mother.

Another standard measure is Animal Unit Month (AUM), which is the monthly forage demand for 1 AU. According to Natural Resources Conservation Service, NRCS. 1 AUM equals 915 lb.

To know how many acres a cow needs, we need to estimate the pasture forage yield. The numbers may lie in a vast range from 0.25 up to 7.5 AUM/ac. Many factors influence these values:

  • Pasture condition;
  • Precipitation zone;
  • Forage type; and
  • Grazing strategy (e.g., rotational grazing).

In our cattle per acre calculator, we focus mainly on the first two factors. Check the table (from Alberta Forage Manual) to see the estimated values of forage production:

Annual precipitation zones
Pasture condition class (yield in AUM/ac)
Excellent
Good
Fair
Poor
250-350 mm
0.75
0.50
0.40
0.25
350-450 mm
1.25
0.80
0.60
0.40
450-550 mm
2.00
1.40
1.10
0.70
550-650 mm
3.30
2.20
1.60
1.10
Irrigation
7.50
5.00
3.75
2.50

How much land does a cow need?

A typical 1000 lb cow with a calf (1 Animal Unit) needs around 0.27 ac (0.11 ha) of pasture in excellent condition and applied irrigation, up to 8 ac (3.2 ha) of pasture in poor condition and low precipitation level. Similarly, a 1300 lb cow with a calf (1.3 AU) requires between 0.34 and 10.3 ac or 0.14 and 4.2 ha land.

How to use cattle per acre calculator?

Let's go together through the step list to understand how our cattle per acre calculator works:

  1. Choose a cattle type you want to graze. If you know the average animal unit of the herd, you can select the Custom option and input your own value.

  2. Enter the total area of the pasture. Check our acreage calculator if you know only the dimensions of the field.

  3. If you don't know the forage yield, choose the annual precipitation and pasture condition. If you do know the number, you can enter the value yourself.

  4. That's all! You can see pasture's cumulative forage production, the total number of cattle, and how many cows per acre can graze on the field in the result section.

  5. You can also play with other parameters (e.g., the utilization rate) according to your needs. Choose the Advanced mode if you know the forage yield and like to modify the lb-to-AUM conversion ratio — by default, it's 915 lb/AUM.

Remaining on cattle-related topics, you may also be interested in checking the cow gestation or animal mortality rate calculator to run your business as efficiently as possible.

How many acres do you need per cow? A sample computation

Now that you know how much land a cow needs and how to use this cattle per acre calculator, let's proceed to an example.

Suppose we want to know the total number of cows that can fit an 800 ac pasture in good condition. We want to keep a herd with an average weight of 1300 lb for the cows with calves. The field's location is relatively wet, which assures the average annual precipitation of 550 to 650 mm. The utilization rate is 50%.

  1. Good pasture condition and precipitation zone provide the average forage yield of 2.2 AUM/ac or 2000 lb/ac.

  2. The total monthly production of the field is 2000 lb/ac * 50% = 1000 lb/ac.

  3. Out of 800 ac pasture, you can collect: 1000 lb/ac * 800 ac = 800,000 lb of forage. We can also write it as: 800,000 lb / 915 lb/AUM = 874 AUM.

  4. An animal equivalent of our cows is 1.3, so the total number of cattle is 874 / 1.3 = 673.

  5. Additionally, we can estimate how many cattle per acre it is (we assume a pair of cow and calf as a single unit): 673 / 800 = 0.84 cattle/ac.

  6. We can also ask the question the other way around — how many acres do you need per cow? Simply find the multiplicative inverse of the previous number: 1 / 0.84 = 1.19 ac per cow.

Tame pasture condition classes explanations

If you want to learn more about different pasture condition classes, check the definitions by Alberta Forage Manual:

Category Excellent Good Fair Poor
Potential yield of the area 75-100% 60-75% 50-60% 33-50%
Production from desirable, adapted grass and legumes 95% 90% 60% Less than 50%
Production from weeds or undesirable plants Less than 5% Less than 10% 20% or more 50% or more
Fertility Program Average to above average Average Below average or non-existent No fertility program

Keep in mind that the values in the table and the results from our cattle per acre calculator are only rough estimations, as the actual yield of a pasture varies for different legumes and grass types. Also, forage production changes throughout the year.

FAQ

How many cows can graze on 5 acres?

You should be able to graze from 2 to 4 cows on average pasture per every 5 acres. However, this number may rise to 20 assuming excellent pasture conditions and applied irrigation.

How many heads of cattle per acre can I keep?

On average, you can have around 0.4 to 0.8 head of cattle per acre if you want to ensure the grazing at the proper rate. Keep in mind that one head of cattle (or one Animal Unit) often refers to the cow and calf pair.

How many cows per acre can I have with rotational grazing?

You should be able to keep between 0.5 and 1.1 cows per acre on average pasture. In general, rotational grazing may increase the cows-per-acre rate up to 30% compared to traditional grazing. However, rotational grazing techniques require at least two paddocks and are usually more expensive.

Wojciech Sas, PhD candidate
Cattle type
Cow, 1300 lbs with calf to 4 months
Pasture area
ac
Do you know the forage production of your field?
No, estimate it for me.
Annual precipitation
350-450 mm
Pasture condition
Good
Check the table for more detailed explanation.
Estimated forage yield
740
lb
/ac
Estimated forage yield
0.8
AUM/
ac
Utilization rate
%
Results
Total forage available
lb
Total forage available
AUM
Total cattle number
Cattle per area unit
0.311
/
ac
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