A Forage Per Acre Calculator is a management tool used by farmers, ranchers, and land managers to estimate the total amount of available livestock feed growing in a pasture or hayfield. By taking a small, representative sample from a field, the calculator scales up the measurement to determine the total yield across a full acre. This calculation is critical for making informed decisions about livestock management, such as setting appropriate stocking rates (the number of animals a pasture can support), planning grazing rotations, and forecasting hay production. Consequently, it helps optimize land use, prevent overgrazing, and ensure a stable feed supply for livestock.
formula of Forage Per Acre Calculator
To calculate your forage yield, you can use a straightforward formula that scales up a small sample to a per-acre basis. For the most accurate results, the "Clip Weight" should be the dry weight of the forage.
- Forage Per Acre Formula (Dry Matter Basis):
Forage Yield (lb/acre) = (Forage Mass per Sample × Area Conversion Factor) / Sample Area - Simplified Step-by-Step Formula:
Forage Per Acre (lb/acre) = (Clip Weight × 43,560) / Sample Area (sq. ft)
Where:
Clip Weight = Weight of forage clipped from a sample area (in pounds or grams converted to pounds). For best results, this should be the dry matter weight.
Sample Area = The size of the area you harvested your sample from, measured in square feet.
43,560 = This is a constant representing the number of square feet in one acre. It is used to scale up the sample weight to a per-acre yield.
Typical Forage Yields by Pasture Type
This table provides general estimates for annual forage production per acre for common pasture types under average management and weather conditions. Yields can vary significantly based on soil health, fertilization, and rainfall. These figures are presented on a dry matter basis.
| Forage Type | Typical Yield (Dry Pounds per Acre per Year) | Notes |
| Alfalfa | 8,000 - 16,000 | High-protein legume, requires good management. |
| Tall Fescue | 4,000 - 8,000 | A durable, common cool-season grass. |
| Orchardgrass | 4,000 - 9,000 | High-quality, palatable cool-season grass. |
| Timothy Grass | 3,000 - 7,000 | Popular for hay, especially for horses. |
| Perennial Ryegrass | 5,000 - 10,000 | Fast-growing and high in quality. |
| White or Red Clover Mix | 4,000 - 8,000 | Often mixed with grasses to improve forage quality. |
| Bermudagrass (Coastal) | 8,000 - 12,000 | A productive warm-season grass. |
Example of Forage Per Acre Calculator
Let's walk through an example to see how the calculation works. A rancher wants to estimate the available forage in a pasture.
First, the rancher marks out a sample area.
Sample Frame Dimensions: 2 feet by 2 feet
Sample Area = 2 ft × 2 ft = 4 square feet
Next, the rancher clips all the forage inside the frame down to grazing height, collects it, and weighs it.
Clip Weight (green weight): 0.5 pounds
To get a more accurate number, the rancher dries the sample completely (in a low-heat oven or microwave) and weighs it again to find the dry matter weight.
Dry Clip Weight: 0.2 pounds
Now, we use the simplified formula with the dry weight.
Forage Per Acre (lb/acre) = (0.2 lbs × 43,560) / 4 sq. ft
Forage Per Acre (lb/acre) = 8712 / 4 = 2178 pounds
Therefore, the rancher estimates there are 2,178 pounds of available dry forage per acre in that pasture at that time.
Most Common FAQs
Livestock nutrition is based on dry matter intake because the water content of fresh forage can vary greatly (from 60% to over 80%). Using dry matter weight removes the water variable, giving you a consistent and accurate measure of the actual nutrients available to your animals.
A single sample is not enough to represent a whole field. For a reliable estimate, you should take multiple samples from across the pasture. A common practice is to walk in a "W" or "Z" pattern across the field, taking 10 to 20 random samples. You can then average the weight of all samples before plugging it into the formula.
The total forage per acre is not the same as the amount your livestock will actually eat. The grazing utilization rate accounts for forage lost to trampling, manure, and selective grazing. A common rule of thumb is "take half, leave half," which implies a 50% utilization rate. To find the truly available forage, you would multiply your total yield (e.g., 2178 lbs/acre) by your utilization rate (e.g., 0.50), which would mean about 1089 lbs/acre are available for consumption.