Pasture Stocking Rate Calculator
Pasture forage demand in AUM from herd size, class, and months.
What it does
Stocking rate decides whether pasture thrives or thins. Too many mouths for too long and plants never recover; too few wastes sun and rain. The animal unit month puts both sides in one currency: how much a standard cow eats monthly against what the land grows.
The tool above prices herd demand in AUM. Enter head, the class equivalent, and months. It returns demand AUM plus animal units. Defaults of 100 cows at 1.15 over 5.5 months open solved at 632.5 AUM, the NDSU worked case.
The standard animal is a 1000 lb cow with young calf at 1.0, eating near 900 lb monthly. Everything else scales: 1200 lb cows run 1.15, bulls 1.5, ewes with lambs 0.2. Fifteen sheep at 0.2 for half a month need just 1.5 AUM, showing how small stock sips.
Supply math mirrors demand. Available pounds divided by 900 gives supply AUM, with half left standing for plant crowns and soil. When demand tops supply, the honest fixes are fewer head, fewer months, or purchased hay, not hope.
Use the table for class equivalents, then run the herd. Extension and NRCS staff sharpen supply estimates from clipping and range sites; the page keeps demand exact.
How to use
- Enter head count.
- Enter the AUE for the class.
- Enter grazing months.
- Read AUM demand first, then AU.
- Compare with pasture supply AUM.
- Adjust head or months to balance.
Formula
- Head
- Head count on the pasture.
- AUE
- Animal unit equivalent vs the 1000 lb cow.
- Months
- Grazing months planned.
- AUM
- Head x AUE x months of forage demand.
Standard animal unit is a 1000 lb cow with calf at 1.0 AUE; adjust by class: 1200 lb cows 1.15, bulls 1.5, ewes with lambs 0.2, rams 0.25. One AUM runs about 900 lb of air dried forage. Compare demand AUM against measured or NRCS estimated supply.
Worked example
Example: 100 cows, 5.5 months
100 cows at 1.15 AUE grazing 5.5 months. Find the AUM demand.
- Animal units: 100 x 1.15 = 115 AU.
- Multiply by months: 115 x 5.5 = 632.5 AUM.
- The herd needs 632.5 AUM of forage.
- Match against pasture supply in AUM.
- Leave half the forage standing for plant health.
- Ewes example: 250 x 0.2 x 5 = 250 AUM.
Reference table
| Class | AUE | Worked demand |
|---|---|---|
| 1000 lb cow with calf | 1.0 | 100 x 1.0 x 5.5 = 550 AUM |
| 1200 lb cows (worked) | 1.15 | 100 x 1.15 x 5.5 = 632.5 AUM |
| Ewes with lambs | 0.20 | 250 x 0.2 x 5 = 250 AUM |
| Bulls | 1.50 | 4 x 1.5 x 2.5 = 15 AUM |
Limits
- Demand side only; supply needs field data.
- Averages hide selective grazing.
- Drought years cut supply sharply.
- Wildlife takes an uncounted share.
Common mistakes
- Using head without AUE scaling.
- Grazing the same months yearly.
- Counting all grown forage as available.
- Ignoring bulls and rams in totals.
- Skipping the 50 percent leave rule.
Try it yourself
Quick checks. Answers sit tucked under each question.
250 ewes at 0.2 for 5 months?
50 AU x 5 months = 250 AUM.
15 sheep at 0.2 for half a month?
3 AU x 0.5 months = 1.5 AUM.
Back-check the example from AU?
115 AU x 5.5 = 632.5 AUM, matching the worked case.
Questions
What is an animal unit?
A 1000 lb cow with young calf, eating about 900 lb of forage a month. Other stock scale by AUE: ewes 0.2, bulls 1.5.
What is the AUM formula?
Animals times AUE times months. Our 100 cows give 115 AU times 5.5 months for 632.5 AUM.
How much forage per AUM?
About 900 lb per AUM (30 lb a day). Divide pasture pounds by 900 for supply AUM.
Demand beats supply?
Demand above supply means destock, shorten the season, or feed hay. Overgrazing bills the next year.
How long can a pasture last?
6 months needs 114.6 AU on the worked supply; 12 months needs half the head. Same forage, different calendars.
Is all grown forage available?
No. Utilization caps near 50 percent, plus trampling and wildlife take shares. The page counts demand; range staff judge supply.
Sources
- USDA NRCS: carrying capacity and stocking rates (North Dakota R1810)
- NDSU Extension: carrying capacity and stocking rates guide