Can I use this Water Softener

I was given a CUNO MCWS100ME softener. I have modern appliances with water saving features, Water saving faucets/shower heads, 4 people in the house, most times. Outside faucets will be isolated from the softener. Is this going to be big enough? Online Calculators say I need 32000 grain, but the book says at max setting its 28500. Another site says a 1.0 volume tank will have 32000 capacity. Any help would be appreciated, Free is always good, but if its not going to work I won't attempt it. Thanks...............Pete