Quick answer: paddock size = what your herd eats in a day × days in the paddock ÷ the forage each acre can give up. Then divide your rest period by days per paddock to see how many paddocks you need. The calculator below does the math and draws your rotation.
1. Your herd
2. Your pasture
How thick is the stand?
Part the grass. If you can see a lot of bare soil, call it thin. If you can’t see the ground at all, it’s dense.
3. Your rotation
Days in each paddock
Spring flush: 20 to 30 days. Summer heat or drought: 45 to 60 or more.
Your rotation, day one
How the grazing calculator works
It starts with what your animals eat. A grazing animal eats roughly 2 to 3.5 percent of its body weight in dry matter every day, so a 1,000-pound cow (one animal unit) needs about 26 pounds of dry forage a day. Multiply by your head count and you have the herd’s daily demand.
Next it works out what each acre can give up on this pass. Pastures hold somewhere around 150 to 450 pounds of dry matter per acre for every inch of height, depending on how thick the stand is. Only the inches between today’s height and the residual you leave count, and the animals won’t eat all of that: some gets trampled, fouled or skipped. The calculator applies a grazing efficiency based on how often you move them, from about 75 percent with daily moves down to about 50 percent with two-week stays.
Paddock size is the herd’s daily demand times the days in each paddock, divided by the usable forage per acre. The number of paddocks is your rest period divided by days per paddock, plus one for the paddock being grazed.
Rest is the lever that matters most
Grass regrows slowly at first, then fast, then slows again as it matures. Coming back too soon catches it in that slow first stage, and the stand gets weaker every pass. That is why rest needs to stretch when growth slows in summer heat or drought. If the calculator says you are short on acres at a longer rest period, that is the real carrying capacity of your place for that season, and the gap has to come from fewer animals, stockpiled forage or hay.
Move more often and the same acres feed more animals. Shorter stays mean less trampling and selective grazing, and every paddock gets a cleaner, more even bite.
Leave enough behind
The residual is the solar panel for regrowth. Most cool-season pastures like fescue and orchardgrass do best grazed no shorter than about 3 to 4 inches. Bermudagrass and other low-growing warm-season grasses tolerate closer grazing. When in doubt, follow the old rule: take half, leave half.
Before you build paddocks
- Plan water first. Each paddock needs water, and livestock graze more evenly when they don’t walk far to drink. Portable tanks and a fast-fill line make small paddocks practical.
- Start with temporary fence. Polywire and step-in posts let you test paddock sizes for a season before you commit to permanent fence.
- Measure, don’t guess. Walk the pasture with a grazing stick or ruler every week. Your forage height and growth rate change faster than you think.
- Keep a grazing chart. Write down the date in and date out of every paddock. After one season you will know your real rest periods and stocking rate.
New to grazing management? Start with what regenerative agriculture is and our guides to rotational and adaptive grazing.
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