Pasture PathStocking rate calculator: AUMs, head and grazing days
How many animals a pasture can carry for the season, worked out from what it grows and what your animals eat — with every assumption on the table where you can change it.
- Usable forage
- 80,000 lb
- Animal unit months (AUMs)
- 101
- AUMs per acre
- 1.27
- One animal eats per day
- 34 lb
- Your herd of 20 lasts
- 118 days
Short: this herd needs about 130 AUMs for the season and the pasture supplies 101. Fewer head, a shorter season or more ground.
An estimate from the numbers you entered. Grass does not read calculators: watch the pasture, and check with a local agrologist or forage association.
How the calculator works
Stocking rate is a balance between what the land grows and what the animals eat.
- Usable forage = pasture size × forage grown per acre × the share you let the animals take.
- What one animal eats = its weight × daily intake as a percentage of body weight.
- Carrying capacity = usable forage ÷ (what one animal eats per day × days in the season).
- AUMs = usable forage ÷ what a 1,000 lb animal unit eats in a month.
The numbers it starts with are only there so the page shows an answer. Change every one of them to match your land and your animals — especially forage grown per acre, which varies more than anything else here.
Getting the size of the pasture right
Stocking rate per acre is only as good as the acres. A pasture on the title as a quarter may graze as 140 acres once the bush, the slough and the yard are taken out. Measure the part that actually grows grass with the acreage calculator.
About stocking rates
What is an animal unit month (AUM)?
The forage one animal unit — a 1,000 lb animal — eats in a month. At 2.6% of body weight a day that is about 790 lb of dry matter. A 1,300 lb cow with her calf counts as about 1.3 animal units, so she needs about 1.3 AUMs for each month she grazes.
How many cows per acre can I run?
It depends almost entirely on how much the land grows and how much of it you are willing to take. The same 80 acres might carry 40 pairs for a season under irrigation and fewer than 10 on dry native range. That is why the calculator asks for forage grown per acre rather than giving one answer for everyone.
Where do I get forage production for my land?
Best is your own: clip, dry and weigh a few square-yard samples through the season. Next best are local figures from a forage association, a provincial pasture guide or a range health assessment for your area. Tame pasture and native range differ by several times, and so do wet and dry years.
What share of the forage should animals take?
A common starting point for tame pasture is half: take half, leave half, so the plants keep enough leaf and root to regrow. Native range and dry years call for less. Whatever you choose, the calculator uses it for every acre.
Does this replace a grazing plan?
No. It is arithmetic to start a plan from, and it assumes the whole season's growth is there to be grazed evenly. A real plan moves animals to match growth — which is what rotational grazing is for.
More tools, and the app they come from
Paddock calculator
How many paddocks a rotation needs and how big each should be.
Acreage calculator
Draw a field on satellite imagery and read off its acres and fence length.
Rotational grazing in Pasture Path
Keep the rotation on your own map: one-tap moves, rest days on every paddock, the next one suggested.
Keep the rotation on your own map
Pasture Path tracks which paddock each group is on, how long every paddock has rested and which is ready next. Free in early access.