this are the normal concrete mixers that you see being pulled by jeeps. its capacity is basically 1 bag of cement + the proportion of gravel and sand like you mentioned 1.2.4 mixture. i learned this when i was planning on renting one mixer when we were building our house ... cheers

Boo!

I'd just recently bought my 1 bagger concrete mixer in a fabrication shop.. before manufacturing it, I'd revised some of its dimensions and steel thickness to withstand my concrete mix requirements..

This is the fastest and easiest way to find out; (for me)

- If you plan to buy, ask the seller of up to what ratio of concrete mix ratio it can hold.. madalas sasabihen nila kung ano timpla ng 1 40 Kg cement.. Ask if it can hold a 1:6:6 and 3 pails of water. Mas maganda kung masubukan for that kind of ratio for 30 minutes. doing so you will see the steadiness, rigidity, mechanical operations for its wearing parts and load weight capacity of the mixer. for the motor driver you will see its power load, alignment, combustion and proportion to its driven.. for that kind of test drive you may see the full capacity for that kind of mixer..(Ewan ko lang kung papaya yun seller lol, pero yun saken napapayag ko naman pero nakailan pako bago may pumayag..hehehehe)

- Then if you plan to rent, only rely on what ratio it can hold to the owner.

I hope I'd gave you the idea you want na medyo strikto nga lang ang dating..