When there is no scale in the field, dimensions and forage type give a solid weight estimate. This tool computes the volume of round, small square, and large square bales and multiplies by a species-specific density so you can plan loads, price by the ton, and avoid overloading a trailer.
How bale weight is estimated
Volume comes from the bale shape, then density converts it to weight:
round bale volume = π × (diameter / 2)² × width (cubic feet)
square bale volume = length × width × height (cubic feet)
weight (lb) = volume × density (lb per cubic ft)Density is set by the forage type you choose. Denser, finer hay such as alfalfa packs more pounds into the same volume than coarse grass hay, so the same bale dimensions can vary substantially in weight.
Typical weight ranges by bale type
Understanding typical weights helps you sanity-check the estimate and plan equipment:
| Bale type | Typical weight range |
|---|---|
| Small square (2-string) | 40–75 lb |
| Small square (3-string) | 85–130 lb |
| Round (4×4) | 400–700 lb |
| Round (5×5) | 800–1,200 lb |
| Round (5×6) | 1,000–1,500 lb |
| Large square (3×3×8) | 700–1,000 lb |
| Large square (4×4×8) | 1,200–1,800 lb |
Actual weight depends heavily on forage species and moisture at baling. Alfalfa sits at the heavier end of each range; mature grass hay at the lighter end.
Worked examples
Example 1 — Round bale of alfalfa (5 ft diameter, 4 ft wide): Volume = π × 2.5² × 4 ≈ 78.5 cubic feet. At 13 lb per cubic foot: weight ≈ 1,021 lb. The same bale in mixed grass hay (9 lb/ft³) would weigh about 707 lb — a difference of over 300 lb on the same size bale.
Example 2 — Large square bale (4×4×8 ft) of alfalfa: Volume = 4 × 4 × 8 = 128 cubic feet. At 12 lb per cubic foot: weight ≈ 1,536 lb. That is roughly three-quarters of a ton per bale, relevant for loader capacity and floor-loading limits in hay storage buildings.
Example 3 — Small square bale (36×18×16 inches = 3×1.5×1.33 ft): Volume ≈ 3 × 1.5 × 1.33 = 5.99 cubic feet. At 10 lb per cubic foot (grass): weight ≈ 60 lb — consistent with bales manageable by hand for horse owners stacking in a barn.
Moisture: the biggest wild card
Hay baled at higher moisture content is heavier per cubic foot but also at risk of heating and molding in storage. These density figures assume hay baled in the dry range (roughly 12–18 percent moisture for large bales, up to 20 percent for small squares). Freshly baled, greener hay can be ten to twenty percent heavier than the estimate predicts. If you are pricing hay by weight and suspect it was baled wet, a hay moisture probe before purchase is worthwhile.
Why round bales aren’t as heavy as they look
A round bale’s weight is not proportional to its diameter — it scales with diameter squared, because volume grows with the radius squared. That has a counterintuitive consequence for the widely quoted “4×4 vs 5×5” bale sizes:
| Round bale (dia × width) | Volume | Weight at 11 lb/ft³ |
|---|---|---|
| 4 × 4 ft | ~50 ft³ | ~553 lb |
| 5 × 4 ft | ~79 ft³ | ~864 lb |
| 5 × 5 ft | ~98 ft³ | ~1,080 lb |
| 6 × 5 ft | ~141 ft³ | ~1,555 lb |
Going from a 4-ft to a 5-ft diameter (same width) adds ~56% to the weight, not 25% — which is why a tractor loader that handles 4×4 bales can be dangerously under-spec for 5×5s. Also note the outer layers of a round bale hold most of the mass: the outer foot of a 5-ft bale contains roughly two-thirds of its volume, so weathering and spoilage on the outside removes far more feed than the thin rind suggests.
When the estimate will be off, and by how much
- Baler density setting swamps species. A modern high-density baler can pack 20–30% more into the same dimensions than an older machine. If you know a supplier bales tight, nudge the density factor up before trusting the number.
- Moisture is a one-way risk. Hay baled wet weighs more now but loses weight as it cures — and can heat, mold, or (in extreme cases) combust in storage. Never pay wet-weight for hay you’ll store dry.
- Net wrap vs twine, and rain. Net-wrapped rounds shed water better than twine-tied ones; a twine bale left in the field can gain then lose weight unevenly as the outer layer soaks and spoils.
- Leaf loss lightens legumes. Alfalfa and clover shatter their nutrient-dense leaves when over-dry at baling, dropping both weight and feed value — a bale that’s all stem weighs and feeds less than the density factor assumes.
- The only truth is a scale. For pricing by the ton or loading near a trailer’s limit, weigh a representative bale; use the estimate for planning, not for a contract.
Practical tips for hauling
- Estimate one bale, multiply by your planned load count, and compare against your trailer’s rated capacity with a safety margin of at least ten percent.
- When making a new hay purchase from an unfamiliar supplier, weigh one bale on a certified scale and adjust your density assumption from the result.
- Round your bale count down, not up, when in doubt — an overloaded trailer risks tire failure and axle damage.
Sources and references
- University of Minnesota Extension — Estimating hay bale weight and forage density — the density-by-species and bale-volume approach used here
- Noble Research Institute — Hay bale weight and quality — practical guidance on moisture, density, and pricing by weight
- Penn State Extension — Hay moisture and storage — why moisture at baling changes the weight and storage risk
Maintained by the Gera Tools editorial team. Weight = bale volume × species density (alfalfa ≈ 11–14 lb/ft³, grass ≈ 8–11); density varies with moisture, baler pressure, and maturity, so weigh a representative bale on a certified scale for critical loads. Last reviewed 2026-07-02.