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 folks 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.

At more than one event, our MU Extension Specialists have asked people to estimate bale weights. Time and again, we see folks 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 for the winter when you really don't.

A lot of those wrong guesses come from neighbor talk. One farmer says their 4x6 bales weigh 1,100 pounds, so the next one figures theirs must be about the same. That's a risky way to do business. Newer balers tend to pack hay tighter than the old ones, and plenty of things—baler settings, forage species, how dry it was when it got rolled up, and storage conditions—can change the final weight. The reality is your hay bales might be shedding weight faster than a steer on Ozempic 😊.

The only surefire way to know? Put it on a scale. But let's be honest—most folks don't have a scale big enough or handy enough to weigh bales, and even fewer sellers are gonna let you weigh bales before you buy. So, you've got to make an educated guess.

Our colleague Dennis Hancock, who now directs the U.S. Dairy Forage Research Center in Madison, Wisconsin, developed Table 1 below. It gives you 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. Here's a simple way to get close (or at least closer):

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

Table 1 Dry Matter (DM) Weight of Common Large Round Bale Sizes at Different Densities

These are just rough estimates, but they're better than no estimate at all. Also, these numbers are based on dry matter weight. To figure out the actual wet weight at the scale, use this formula:

For example, if the table says a bale has 1,020 lbs of dry matter and the hay is at 15% moisture, the actual weight at the scale would be:

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 for winter, a little math and a little common sense can go a long way toward making sure you don't come up short.