Crop farming · Hay
Hay bale weight and yield.
Bale size and firmness give pounds per bale. Bales cut from a field give tons per acre, and herd size gives the bales you need for winter feeding.
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Bale weight and yield
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How much does a hay bale weigh?
Bale weight = bale volume × density. The volume of a round bale is 3.14 × (diameter ÷ 2)² × width; a square bale is width × height × length. Penn State Extension, using estimates from Dennis Hancock, gives 9 pounds of dry matter per cubic foot for a loose bale, 10 for a bale that still gives, 11 for a fairly tight bale and 12 for a really tight one. The method applies to small square, large square and round bales.
Worked example. A bale 4 feet wide and 5 feet in diameter holds 2.5 × 2.5 × 3.14 × 4 = 78.5 cubic feet. At 12 lb per cubic foot it weighs 942 pounds; at 9 it weighs 706.5 pounds. If 50 of the 942-pound bales come off a 10-acre field, the yield is 50 × 942 = 47,100 lb, divided by 10 acres and 2,000 lb per ton, about 2.4 tons per acre (2.36 exactly).
Bales for winter. Penn State's example is 25 beef cows at 30 lb of hay a day for 150 days: 112,500 lb. With 706.5-lb bales that is 159 bales, and with 942-lb bales 119.4, so 120. Penn State's own figure rounds the first to 159, and this tool says "buy 160" because it rounds up. Penn State also notes that many producers grossly overestimate bale weight, which can leave them short of hay in late winter.
The weights are dry matter. Enter a moisture percentage to get the as-baled weight, dry matter divided by (1 minus moisture), which is plain arithmetic rather than a Penn State figure.
Frequently asked questions
How much does a 4x5 round bale weigh?
A bale 4 ft wide and 5 ft in diameter is 78.5 cubic feet. Penn State's density estimates of 9 to 12 lb of dry matter per cubic foot give 706.5 to 942 pounds.
How do I estimate hay yield per acre from bales?
Multiply the number of bales by the weight per bale, then divide by the acres and by 2,000 lb per ton. 50 bales of 942 lb from 10 acres is about 2.4 tons per acre.
How many bales does a cow need for winter?
Penn State figures about 30 lb of hay per day for a beef cow, so 150 days is 4,500 lb. With 942-lb bales that is about 4.8 bales per cow for the winter. Your cow size and hay quality change this.
Is the weight dry matter or as-baled?
The Penn State densities are pounds of dry matter per cubic foot. Enter a moisture percentage if you want the weight on the scale.
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Not professional advice
Bale weights are estimates. Weigh a few representative bales on a scale before relying on them for feeding or selling.