A bale is a compressed mass of forage whose density sets both its weight and how well it sheds weather. Denser bales store better and dry more slowly, and the trade runs both ways.
Bale: density, weight, and the storage loss it buys
window HAY WINDOWchecked 2026-09-16responsible Windrow Field Manual (a named masthead, not a person)
[['Loose, soft core', 'Fast drying, forgiving moisture band', 'High storage loss, low weight per bale'], ['Medium', 'A working compromise', 'Nothing sharply'], ['High, hard core', 'Low storage loss, high weight per bale', 'Narrow moisture band, slow cooling']]
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Weight is density times volume, plus water
Two bales of the same size can differ by a third in weight. The difference is density, and the practical consequence is that a bale count is not a tonnage. Anyone who has bought hay by the bale and then by the ton has met this problem.
| Bale type | Typical diameter × width | Typical mass | Notes |
|---|---|---|---|
| Large round, soft core | 1.2 m × 1.2 m | 250–350 kg | Forgiving on moisture |
| Large round, hard core | 1.5 m × 1.5 m | 600–900 kg | The core is the risk |
| Large square | 1.2 m × 1.2 m × 2.4 m | 500–900 kg | Stacking compounds heat |
| Small square | 0.4 m × 0.5 m × 0.9 m | 15–25 kg | Highest surface per kg |
Storage loss is where density pays
Weathering loss happens at the surface of the stack and at the surface of the bale. A dense bale presents less surface per tonne, sheds water better, and slumps less, so it holds its shape and its weatherproof thatch. The literature puts the spread between the best and worst outdoor storage practice at a large fraction of the dry matter, which is why density is worth paying for.
The same density that reduces weathering loss reduces the bale's ability to shed the heat of respiration. Denser is better right up to the point where the moisture is a little too high, and then denser is worse, and worse quickly.
Boundary: a bale is not a stack and not a baleage tube
A bale is one unit. A stack is a set of bales whose interior behaves as a single larger mass with a much worse surface-to-volume ratio. A baleage tube is a sealed, wet, anaerobic system that shares the word bale and none of the arithmetic.
The misreading to avoid: treating a stack of hard-core bales as if it were a row of soft-core bales. The stack's interior reaches temperatures the individual bales never would, and the moisture that was safe per bale is not safe per stack.
The manual's contestable position
The manual holds that for anyone storing outdoors in a wet climate, the correct next purchase is density at the baler rather than a better cover. A cover on a loose bale protects a large surface; density removes the surface in the first place. The two are not equivalent and the difference is measurable.
Where the numbers come from
- S1Hay Storage and Feeding Losses (Publication 2540), Mississippi State University Extension Servicesupports the storage and feeding losses attributed to bale density and cover
- S2Hay Storage (Forage Facts 34), Kansas State University Agricultural Experiment Stationsupports the relationship between bale density, moisture and storage loss
- S3How Much Does That Bale Really Weigh? Feeding and Fertilizer Implications, Penn State Extensionsupports the bale-weight figures used to turn bale counts into tonnage
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Put this page down Put this page down when you know the mass of your bales, not just the count. Tonnage is the number that pays.