Hay Bale Weight Calculator NZ

This estimates what a bale weighs from its dimensions and how tightly it was rolled, converts that into kilograms of dry matter, and turns a bale price into a cost per kilogram of actual feed. That last figure is the one that settles arguments, because a price per bale compares neither weight nor water. Baleage carries far more water than hay, commonly around 45 percent dry matter against 85 for hay, so two bales that look identical in a paddock can differ by hundreds of kilograms and by much more than that in feed value. The other thing worth watching is diameter, because a round bale is a cylinder and volume depends on the radius squared. Going from a 1.2 metre bale to a 1.5 metre bale of the same width sounds like a quarter more bale and is actually 56 percent more, so a price that looks a little higher for the bigger bale can easily be the cheaper feed. Density is where the estimate is softest: it varies with the baler, the crop and the moisture, so the defaults here are starting points and a weighbridge ticket beats any of them. If you have weighed a bale, enter that weight directly and skip the dimensions.

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m
m
m
kg/m3
%
$
kg
244 kg
estimated weight of one bale
Dry matter in it208 kg DM
Volume1.36 m3
Cost per kg DM$0.41
Cost per tonne DM$409

Density is the softest figure here. It varies with the baler, the crop and the moisture, so a weighbridge ticket beats any estimate.

No standard bale weight is supplied, because there is no standard bale. Density defaults are starting points to change, not figures to rely on. Dry matter percentages differ sharply between hay and baleage, which is exactly why the comparison has to be made per kilogram of dry matter.

How it works

A round bale is a cylinder, so its volume is pi times the radius squared times the width. A square bale is simply length times width times height. Volume multiplied by density gives the weight, and weight multiplied by the dry matter percentage gives the kilograms of actual feed in the bale. Dividing the bale price by that dry matter figure gives cost per kilogram of dry matter, which is shown per tonne as well since that is how feed is usually traded. If you enter a weighed bale, that weight is used instead of the estimate and the dimensions only affect the volume shown.

Why per kilogram of dry matter is the only fair comparison

Because a bale price hides two variables at once. The first is size, and the radius squared relationship means the difference between bale sizes is larger than it looks. The second is water: hay at 85 percent dry matter and baleage at 45 percent are being sold by the same word, bale, while delivering very different amounts of feed. Cost per kilogram of dry matter removes both, and it is also the unit that lets bought feed be compared with the cost of growing your own, which is the comparison that usually matters most.

Worked example

A round bale 1.2 metres across and 1.2 metres wide has a volume of 1.36 cubic metres. At 180 kilograms a cubic metre that is 244 kilograms, and at 85 percent dry matter it holds 208 kilograms of feed. At $85 a bale the feed costs $0.41 a kilogram of dry matter, or $409 a tonne. The same bale made 1.5 metres across instead would hold 2.12 cubic metres, which is 56 percent more feed from a bale that is only 25 percent wider in diameter, so at anything under $133 it would be the cheaper feed of the two.

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Data sources: no standard bale weight or density is supplied, because bale weight varies with the baler, the crop and the moisture. The geometry is exact; everything else is yours to enter or to weigh.

Frequently asked questions

How much does a round bale of hay weigh?

It depends on the size and how tightly it was rolled, which is why a single figure is misleading. Weight is volume multiplied by density, and a bale of given dimensions can vary considerably between balers and between crops. Baleage is much heavier than hay of the same size because it carries far more water, commonly around 45 percent dry matter against 85 percent for hay, so two identical looking bales can differ by hundreds of kilograms.

Why does the volume of a round bale go up so fast with diameter?

Because volume depends on the radius squared. Going from a 1.2 metre bale to a 1.5 metre bale of the same width is a 25 percent increase in diameter but a 56 percent increase in volume, and therefore in weight and in feed. That is why comparing prices between bale sizes without converting to weight is one of the easiest ways to overpay for feed.

How do you compare hay and baleage prices fairly?

Convert both to cost per kilogram of dry matter. A bale price on its own compares neither weight nor water content, and baleage carries a great deal more water than hay. Dividing the price by the kilograms of dry matter in the bale strips both out and leaves the only number worth comparing, which is what you are paying for actual feed.