SDSU Extension Grazing Calculator

Use this when you know how long you want to graze


Use this when you know herd dynamics and want how many days

The goal of this app is to help livestock producers calculate stocking rates and develop grazing management plans for their pastures. The information below is how the calculations are performed.

Input Variables

  • Number of Acres = The actual acres within each paddock you want to graze during the season
  • Average Forage Production* = The dry matter (lbs./acre) production estimate for the pasture
  • Harvest (Grazing) Efficiency** = Percentage of forage actually ingested by the animals from the total amount of forage produced. See illustration.
  • Number of Individual Animals = The number of animals you plan to graze.

Forage Demand

Forage Demand (% body weight/day) as a general rule of thumb for stockers, feeders, and bulls is 2.5% of body weight

Forage quality, though, adjusts the amount a cow will consume. For example, high quality forage (>59% TDN) equates to high digestibility, meaning that the cow will intake about 2.7% of her body weight if she is lactating. In contrast, low quality forage (<52% TDN) equates to low digestibility and that same lactating cow will consume about 2.2% of her body weight.

  • High quality forage (>59% TDN)
    • Examples: Early-bloom and mid-bloom legume hay, pre-boot stage grass hay, lush pasture, silage
  • Medium quality forage (52-59% TDN)
    • Examples: Dry summer/fall pasture, late-bloom legume hay, early-bloom grass hay
  • Low quality forage (<52% TDN)
    • Examples: Dry winter forage, mature legume and grass hay, straw

Calculation Equations

  • Total Forage Production = Avg. Production x Acres
  • Total Forage Allocated for Consumption = Total Forage Production x Harvest Efficiency
  • Number of Individual Animals Allowed = (Total Forage Allocated for Consumption/Days) / (Animal Weight * Forage Demand)
  • Total Herd Days in Pasture = Total Forage Allocated for Consumption / (Animal Weight * Forage Demand * Number of Animals)


  • Jameson Brennan, Assistant Professor & Livestock Grazing Specialist, South Dakota State University University,
  • Krista Ehlert, Assistant Professor & Extension Range Specialist, South Dakota State University,

Other Great Information

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Extension Link

*Forage production estimates can be gathered by several ways. First, you can clip and weigh vegetation in your pastures or use a grazing stick to determine the amount of production. Second, you can visit the USDA NRCS Web Soil Survey online. You will need to input your 'Area of Interest' and then click on the 'Soil Data Explorer' Tab. The left side of the screen displays 'Suitabilities and Limitations Ratings' - click on 'Vegetation Productivity' and then you can select 'Range Production' under 'normal,' 'favorable,' and 'unfavorable.' For help with either of these methods, contact SDSU Extension or your local NRCS Field Office
**Harvest (Grazing) Efficiency can range from 25% to 40% depending on management intensity. In order to maintain adequate forage production and health, the target utilization level for many species is about 50%. This means that 50% of the plant weight remains behind in the pasture, and 50% is available for use - of that 50%, approximately 25% is wasted, leaving 25% that ideally is ingested by the animal. This harvest efficiency can be increased through management intensity; however, it is generally not recommended to go above 35%. Image taken from: