To calculate pasture stocking rate, multiply grazable acres by pounds of forage dry matter per acre and by grazing efficiency (25 to 40 percent), then divide by each animal's daily intake (about 3 percent of body weight for a cow-calf pair) times days in the season. Round down, then check the grass mid-season.
That is the whole calculator in one sentence. The rest of this guide is about where each of those numbers comes from, because that is where most stocking plans go wrong. Nobody gets the division wrong. They get the inputs wrong.
Ask around at the sale barn and you will hear one cow per two acres, one per five, one per ten. Every one of those numbers is right for somebody's ground in somebody's year, and wrong for most everybody else. A rule of thumb hides three things that decide the answer:
There is a fourth problem hiding in the word "cow." The standard planning unit, the animal unit (AU), is a 1,000-pound cow with or without a calf up to weaning. A lot of today's beef cows weigh 1,300 to 1,500 pounds, and South Dakota State University's own grazing examples use a 1,500-pound cow. If your cows weigh 1,400 pounds, each one is 1.4 animal units. A "one cow per X acres" rule built on a 1,000-pound cow undercounts what a herd like that eats by 30 to 50 percent.
Two terms are worth keeping straight. Carrying capacity is what the land can support while holding the forage base steady. Stocking rate is what you decide to put on it. The calculator's whole job is to make the second match the first.
Do this on the back of a feed-store receipt. Every blank is something you can measure, look up, or take from extension planning values.
A. Grazable acres: ______ ac
B. Forage grown, lb dry matter per acre: ______ lb/ac
C. Grazing efficiency (0.25 to 0.40): ______
Usable forage = A x B x C = ______ lb
D. Animal weight: ______ lb
E. Daily intake (0.03 for pairs): ______
F. Days in the grazing season: ______ days
Need per head = D x E x F = ______ lb
Head you can carry = usable forage / need per head = ______
Round DOWN.
Now let's fill in each line properly.
Start with the acres the animals can and will graze, and subtract everything else: timber, heavy brush, ponds and creek bottoms that stay wet, building sites, and lanes. Lanes add up faster than people expect. The Noble Research Institute points out that one mile of 20-foot-wide ranch road is 2.4 acres. Run that across a few miles of lanes and alleys and you have quietly lost a paddock.
The most common error here is using the number on the deed, the lease, or the tax bill. Those describe the property, not the grass.
Get the real number before you do any math. Our free Field Boundary and Input Calculator lets you search your location, then draw field boundaries on a satellite map and read off the acreage. To use it for this, draw only the grazable part of each paddock. Trace around the timber, leave out the pond, skip the lane. Add the paddocks up and that total goes on line A. The tool measures the land; the stocking math happens here in this guide.
This is the number that varies most from farm to farm, so it is the one you most need from your own ground. There are three ways to get it, from quickest to most precise.
A grazing stick is a yardstick printed with conversion tables. Your local NRCS or conservation district office is a good place to ask for one. Walk the pasture and measure average leaf height, not seed heads, at 15 to 20 spots or more. Multiply the average height by the pounds of dry matter per inch per acre for your kind of stand.
SDSU Extension's planning values (pounds of dry matter per inch per acre):
| Pasture type | Normal stand | Excellent stand |
|---|---|---|
| Cool-season grass + legume | 150 - 250 | 250 - 350 |
| Cool-season introduced grass | 100 - 200 | 200 - 250 |
| Native warm-season grass | 100 - 250 | 250 - 350 |
Washington State University's method uses a hoop with a 93-inch circumference. Toss it, clip everything inside that the animals will eat, leave out last year's dead stems, and dry and weigh it in grams. Net dry grams times 20 gives you pounds per acre. Repeat several times across the pasture and average. If you weigh it green, convert with dry matter by growth stage. For cool-season grass, WSU uses about 35 percent dry matter before heading, 45 percent headed out, and 60 percent at seed ripe.
The free NRCS Web Soil Survey reports forage or range production in pounds per acre for favorable, normal and unfavorable years, by soil map unit. It is the right starting point for ground you have not grazed yet, and a good sanity check on clipping. WSU's advice is blunt: if the soil survey says the site tops out at 750 pounds and your clipping says 3,000, check your work.
Plan on the unfavorable-year number, or close to it. Treat a good year as a bonus you can stockpile or put up as hay. That is the honest drought hedge, and it is far easier than selling pairs into a dry August.
This is the most confused input in the whole calculation, because two different conventions get used and both are correct.
"Take half, leave half" is a utilization rule: about 50 percent of the forage gets removed. But removed is not the same as eaten. University of Wyoming Extension walks through 1,000 pounds per acre: 500 pounds stays behind for regrowth and roots, about 250 pounds is lost to trampling, fouling, insects and wildlife, and about 250 pounds ends up in livestock. So 50 percent utilization works out to roughly 25 percent eaten.
Grazing efficiency (also called harvest efficiency) is the share of the whole season's growth that ends up inside the animals. That is the number the calculator wants on line C. SDSU's table for a 180-day season:
| Grazing system | Season-long efficiency |
|---|---|
| 1 pasture, continuous | 25% |
| 2 pastures | 30% |
| 4 - 8 pastures | 35% |
| 12+ pastures | 40% |
Why does rotation raise the number? Cattle that are moved often graze more evenly and waste less. Oregon State University reported per-grazing utilization of about 70, 50 and 40 percent when cows were moved every 3, 7 and 14 days. It also noted that four paddocks give each one 75 percent rest and eight give 87 percent, so most of the rest benefit comes with just four to eight paddocks. Those are per-grazing figures, not season-long efficiency, so keep them out of the formula. They explain why the SDSU numbers climb with paddock count. Rotation gets you more, not double.
Do not discount twice. SDSU's season-long efficiency already accounts for the residual you leave behind. If you subtract residual height and then also apply 25 percent, you will under-stock and leave grass on the table.
Plan on 3 percent of body weight per day in forage dry matter for a cow-calf pair. WSU, SDSU and Noble all use 3 percent for pairs. WSU's reasoning is that it builds in a margin and partly covers what the calf grazes. Dry cows can be planned closer to 2.5 percent.
A 1,300-pound cow at 3 percent needs 39 pounds of dry matter a day. A 1,200-pound cow needs 36. (One widely shared extension sheet prints 40 for the 1,200-pound cow; the arithmetic is 36.)
The AU rating for other stock, from University of Wyoming and University of Georgia extension tables:
| Animal | Animal units |
|---|---|
| 1,000-lb cow, with or without calf to weaning | 1.0 |
| Cow, any weight | weight / 1,000 (1,400 lb = 1.4) |
| Mature bull | 1.35 |
| Mature horse | 1.25 |
| 700-lb yearling | 0.7 |
| Mature sheep | 0.20 (5 sheep = 1 AU) |
| Goats | 5 goats = 1 AU |
Know your real cow weights. A guess of "about 1,200" on a herd that actually averages 1,400 is a 17 percent error on the demand side before you start. If you want a hands-off way to track it, see our guide to walk-over weighing systems for cattle.
Here is the full calculation for a 40-acre pasture. The forage number and season length are example values chosen for the arithmetic. Use your own.
| Step | Input | Value |
|---|---|---|
| A | Grazable acres (drawn in the field calculator, timber and lane left out) | 40 ac |
| B | Season forage production (example only) | 2,000 lb DM/ac = 80,000 lb |
| C | Grazing efficiency, 4 - 8 paddock rotation | 35% = 28,000 lb usable |
| D x E | 1,300-lb cow x 3% | 39 lb/day per pair |
| F | Season length (example only) | 150 days = 5,850 lb per pair |
| Result | 28,000 / 5,850 | 4.8, so carry 4 pairs |
Run the same field grazed continuously at 25 percent efficiency: 20,000 pounds usable divided by 5,850 is 3.4, so 3 pairs. Same grass, same rain, one more pair carried with a basic rotation. That is the practical payoff of cross-fencing and moving cattle.
Notice that 4.8 rounds down to 4, not up to 5. That is deliberate. The unrounded number assumes an average year, a perfectly measured stand and cattle that weigh exactly what you wrote down. Rounding down is your margin for being wrong on any of those. At 4 pairs on 40 acres, this example works out to about 10 acres per pair, which is nothing like "one cow per two acres."
People ask the same question three different ways. The same numbers answer all of them.
How many head can I carry? Usable forage divided by (daily need per head x days). That is the example above.
How many days will this paddock last? Usable forage divided by the herd's daily need. WSU's example: 250 cows at 1,200 pounds and 3 percent eat 9,000 pounds a day, so 225,000 pounds of usable forage lasts 25 days.
How many acres do I need for the herd I want? Herd season need divided by (efficiency x production per acre). SDSU's example: 100 cows at 1,500 pounds, 3 percent, 150 days need 675,000 pounds. At 25 percent efficiency and 2,000 pounds per acre, that takes 1,350 acres. Using the 40-acre example above, carrying 6 pairs instead of 4 would take about 50 acres at 35 percent efficiency.
With the national herd small (USDA counted 86.2 million cattle and calves on January 1, 2026, with beef cows down 1 percent), a lot of people are holding back heifers or buying pairs. Adding head without re-running these numbers is how good pasture gets overgrazed in a single season.
An animal unit month (AUM) is the forage one AU eats in a month. The trouble is that published values differ: University of Wyoming uses 750 pounds of air-dry forage (2.5 percent of body weight for 30 days), while the NRCS planning intake of 26 pounds of oven-dry forage a day works out to 780 pounds. Wyoming Extension's advice is to agree on the AUM definition in writing before signing a lease.
Bill by weight, not by head. A 1,300-pound pair grazed for 5 months is 1.3 AU x 5 = 6.5 AUMs, not 5.
The calculator is a starting point. The grass gets the final vote.
Stocking rate is not a number you look up. It is five numbers you measure or look up, multiplied and divided, then checked against the grass. Get the acres right first, because every error there carries straight through to the answer. Draw your grazable acres in the Field Boundary and Input Calculator, work the blanks above, and round down. If you are ready to track it paddock by paddock through the season, our roundup of pasture management technology covers the apps that log grazing days and rest periods for you, and virtual fencing and GPS tracking can make smaller paddocks practical without more wire.
Multiply grazable acres by forage dry matter per acre, then by grazing efficiency: 25 percent for continuous grazing, up to 40 percent with 12 or more paddocks. Divide that by each cow's need, which is body weight times 3 percent times the days in your season. The result is head you can carry. Round down and check residual height mid-season.
There is no single answer, because it depends on how much forage your ground grows and how you graze it. In one worked example with 2,000 pounds of dry matter per acre, a 1,300-pound cow, a 150-day season and a four-to-eight paddock rotation, each pair needed about 10 acres. Low-rainfall range can need many times that. Run the numbers with your own production.
An animal unit (AU) is a 1,000-pound cow with or without a calf up to weaning, which NRCS plans at about 26 pounds of oven-dry forage a day. Other animals are rated against it: a 1,400-pound cow is 1.4 AU, a mature horse 1.25, a mature bull 1.35, and five sheep or five goats equal one AU.
Yes, by improving how much of the grass the cattle actually eat. SDSU Extension plans season-long grazing efficiency at 25 percent for one continuous pasture, 35 percent for four to eight paddocks, and 40 percent for 12 or more. On the same 40 acres, that difference can mean carrying four pairs instead of three. It helps, but it does not double carrying capacity.
Plan from the start on the unfavorable-year forage number from the NRCS Web Soil Survey, so a dry year does not catch you overstocked. During the season, measure with a grazing stick and protect residual height, at least 4 inches on cool-season grass and 6 to 8 inches on native warm-season grass. When growth falls behind plan, sell or move animals early.
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