If it is a perfect rectangular prism you do length*width*height.
You would find the volume of one bale of hay an then multiply the volume by the number of bale or an estimate of the number.
When you cut grass in the meadow, this is called mowing the grass and if the grass is to be used for hay it is called mowing the hay or a 'hay mow'.
hay or grass(Y)
pasture grass and hay
all dried grass is called hay. it is where you dry fresh cut grass make it into hay.
Timothy is a grass hay
Oh, dude, I've stacked like a gazillion hay bales, you know, just casually building my own little hay fortress. But seriously, I've stacked enough hay to make a cow jealous. Like, it's basically become my new workout routine.
There is grass in that bundle of hay because that's what was cut and gathered up as hay. A little extra grass in a bale or bundle of hay isn't going to hurt anyone or anything. Pretty sure the cows will enjoy it just as much as there was no grass in the hay you're feeding them.
Hay
Grass is cut by a swather, haybine or a scythe then let to lay in the field to dry naturally by the heat of the sun and the wind. Once the grass is dry enough (with only around 10 to 20 percent moisture), it is raked then baled or stacked. The bales or stacks are then placed in a shelter (mainly for square bales), or stacked in a way that it slicks off moisture. Stacks are often covered to protect them from excess moisture.
Orchard hay is a type of grass hay grown from orchard grass. This type of hay is excellent horse feed, but can be fed to most any grazing animal.
If they were given a choice, they'd choose grass over hay any day. But during the winter months when there is no grass to eat, hay is their primary choice.
grass+fire=hay