Cement Mixer Question

[Brake]

I recently got a pto driven cement mixer. It is really old and has no manufacturer tag. It got me wondering how do you measure the volume? It would be easy enough if it was a cylinder but it is the typical mixer shape of a cone on top, barrel in the middle, and concave back-end.
It got me thinking how are cement mixers measured? You only use half of it anyway at most since it is on an angle when in use. So it got me wondering how they are measured.

 

[flyingblind]

By the Pound or the Yard

 

[Firebrick43]

You can put it vertical, and fill it with water by a bucket of known volume.

Or you can break the shape down into 3 or 4 separate sections and use a volume calculator to measure it.

https://keisan.casio.com/exec/system/1223372110

 

[dscheidt]

It's the total volume of the drum. Batch volume is about 2/3 that, but some smaller electric mixers are limited by the motor to about 1/2 or even a bit less that capacity.

 

[Shiftless]

You can put it vertical, and fill it with water by a bucket of known volume.

Or you can break the shape down into 3 or 4 separate sections and use a volume calculator to measure it.

https://keisan.casio.com/exec/system/1223372110

That is how you do it.
As others said, you can’t fill it all the way with concrete and expect it to work at all.
If you hate math, just post the diameters and the vertical distances I sketched here and somebody will figure out the cubic feet or gallons or whatever you need.