The skinny on what your hay bales really weigh

Ask five farmers how much their hay bales weigh, and you’ll probably get five different answers – none of which are backed up by a scale ticket.

That’s because most farmers think they know their bale weights, but more often than not, they’re guessing, and when you’re buying hay by the bale instead of by the ton, those guesses can cost you real money.

Extension specialists with the University of Missouri (MU) often ask people to estimate bale weights during events. Time and time again, they see farmers overestimate bale weights, sometimes by a couple hundred pounds. That can lead to errors of 15% to 20%, which is a pretty steep tax if you’re buying. Worse yet, it can lead to thinking you’ve got enough hay when you really don’t.

Many of those wrong guesses come from what extension specialists call “neighbor talk.” If one neighbor says his bales are 1,100 pounds, the next one assumes theirs must be about the same, which is a risky way to do business.

Newer balers tend to pack hay tighter than the old ones, and other factors – baler settings, forage species, how dry it was when it got rolled up and storage conditions – can change the final weight.

There is only one surefire way to know what hay weighs. Put it on a scale. However, most buyers and sellers don’t have a scale big or handy enough to weigh bales. Plus, few sellers allow the buyer to weigh the hay before buying.

Dennis Hancock, who directs the U.S. Dairy Forage Research Center in Madison, Wisconsin, developed a method to give an idea of what bales weigh based on their size and how tightly they’re packed. The tricky part is bale density – it varies a lot. For instance, a loosely packed 5X5 bale would have about 880 pounds of feed; a tightly packed one has nearly 1,200 pounds. Here is a simple way to estimate bale density:

• Loose bales that depress and don’t spring back: Probably 9 pounds of dry matter (DM) per cubic foot or less
• A little firmer but still gives when you press it: Around 10 pounds of DM per cubic foot
• Good and solid, but you can still dent it with a spike: About 11 pounds of DM per cubic foot
• You can barely get the hay spike in: Likely 12 pounds of DM per cubic foot or more

To know how many cubic feet are in a round hay bale, you need to know its volume. That takes a bit of math. First, divide the diameter (or height) in feet of the bale by two. Square that number. Then multiply that by 3.14 and then multiply that result by the bale width in feet. The result is the volume of the bale in cubic feet.

For example, a 5X5 bale has 98 cubic feet of hay: (5/2)^² x 3.14 x 5 = ~98. Loosely packed bales have a density of 9 pounds per cubic foot of hay, which equates to 880 pounds of dry feed. A tightly packed bale at 12 pounds per cubic foot would have almost 1,200 pounds of dry feed. Hancock’s figures are rough estimates, but they’re better than no estimate at all.

It’s easy to misjudge bale weights, and those mistakes add up whether you’re buying hay or figuring out how much you’ve got stored. Some math and a little common sense can go a long way toward making sure you don’t come up short.

For more information, see the University of Missouri Integrated Pest Management newsletter article.

Reprinted with permission from the University of Missouri.