Readily decomposable organic matter - compost, leaf mold, coffee grounds, etc. - are not good materials to include in any kind of significant amounts for a potting soil. Neither is 'soil', if you mean by that garden soil. Most potting soils are what are termed 'soil-less' mixes - they do not contain any sort of real soil. It is too dense and with insufficient drainage to provide what container grown plants require. In fact, I'd leave out much of what you are currently using in your potting soil mix :-)

If you do not want to fill up large containers with all potting mix, there are methods of filling up a portion of the container that will still provide proper drainage. The coffee grounds won't. I'd suggest you try posting this same question in the Container Gardening forum - you'll get some excellent recommendations for quality potting soil recipes that hold up properly over time and provide fast drainage and high aeration - absolute requirements for container gardening. And a number of suggested methods for partially filling large containers with something other than potting soil yet still maintaining the fast drainage you need.

I agree, no need for the grounds. Mixing the most light mix possible that has drainage and water retention. Compost,peat,perlite are basic soil potting mixs. If you can find a good source of pine bark fines or orchid bark, I would go with Al's 5-1-1.

The link below might provide some information.

Here is a link that might be useful: Coffee grounds as potting soil

If what you are wanting to just fill up volumn & what you are planting is not too deeply rooting, I would fill the bottom of your big container with packing peanuts or plastic water bottles. I do that successfully every year with annuals planted in big pots.

I've some rather serious links at Chemicals in Coffee. The ones down about Dec 5th are quite interesting - it will help to have a couple of semesters of college chemistry. I have come to the conclusion that container plants, except for tough office plants in office situations where slow growing is desirable, should not be planted directly in nothing but coffee grinds only.

There is a soil mix company here in S.C., that mix up potting soil for nurseries. They have been using coffee waste(green beans,roasted bean, ground beans & chaff), but mostly chaff.
The coffee is not used, but in its pure form. His costumers love the mix. He is picking up the coffee waste every week. I have many tons of the same coffee waste. The only thing that is new is that the grass is greener & taller from the waste.
A 4'X 4'X 8'is laying on it's side for 4 months in the open.
The grass around it is taller & greener then grass 4 feet away.
I have no slugs in my garden or orchard, now that I use coffee waste, I did before. I have not seen a snail or slug in 5 years now.
I may be my good looks & winning personality, but I think it is the coffee waste.