Estimating Bucket Capacity for Wheel Loaders

Remember when you were in grade school and you had to solve math “story problems”? Who really cared when the two trains coming from different directions at different speeds would meet up in Peoria? Now, though, you’re working with heavy equipment and you face real-life math problems, some of them not so easy. For example, how do you estimate bucket capacity for wheel loaders?

You will recall that the formula for calculating volume is height x width x depth. But the bucket on your 2.5 wheel loader isn’t a nice, neat box, is it? Nope, it’s a weird shape – sort of square, but sort of round. That’s a different story when it comes to doing the math.

You multiply the bucket’s cross-sectional area by its length.

We’ll explain

That “2.5-yard” capacity is actually the amount of material the bucket can hold inside plus the amount heaped up above the rim. In fact, the official designation is Heaped (or Rated) Capacity. According to the Society for Automotive Engineers (SAE), heaped volume depends on “the angle of repose of the material being handled.” In other words, sand and rock or debris will each be different.

The SAE says that, in general, the angle of repose for a wheel loader bucket is 2:1. (For comparison, the typical angle for a hydraulic excavation bucket is 1:1.) So, in real life, you need to figure the actual capacity for the actual material your wheel loader is moving.

If you’re old enough, you may have used a planimeter in the past – a measuring device specifically designed to assist with these calculations. Today, thanks to the advent of computers and CAD software, you can probably use technology to duplicate the shape of your bucket and quickly figure its area. Nonetheless, you may still need to do some math the old-fashioned way – by hand.

Here’s how

Going back to math class, you’ll remember that, to determine the area of an odd shape, you have to divide it into sections, then calculate the area of each section and add them together. That total is the cross-sectional area you’ll need to know in order to figure the bucket’s capacity (volume).

•  Trace an outline of your bucket on a big piece of paper. You want the interior shape because that’s where the material goes. Make it as accurate as you can.
• Draw a baseline between the spillboard and the cutting edge. Now draw a perpendicular line from the center of your baseline. If you’re using the 2:1 heap ratio for your wheel loader bucket, make the perpendicular line 1/4 as long as your baseline. Now draw two more lines connecting each end of the baseline to the perpendicular line, and you have two adjacent triangles that represent the heap.
• Draw a series of vertical and horizontal lines over your “bucket.” Because your 2.5-yard bucket is small, draw your grid lines every 6”. That way, each square will represent .25 square feet.
• Number all the whole squares so you have a total count. Then eyeball the partial squares, adding them together to approximate whole squares, and count those new squares. You don’t have to be precise with this – you may be over or under with your individual estimates, but it will all even out.
• Add the total of new squares to your original whole square total. Then figure the square footage. (Above, we noted that using a 6” grid gives you .25 square feet per square.) This is your cross-sectional area.
• Finally, to calculate the volume, multiply the cross-sectional area by the length of the bucket, in feet.

And there you have it – estimated bucket capacity for your 2.5-yard wheel loader.