Each annual will cover a different area...
It may be over kill....but I make a graph and draw the plants in the picture.
You sayt 10 inches??? I think that's a bit sparse.
Tell me what you are considering and I can give you recommentations as to how close to plant. For example, petunias should be planted closer than cleome....

Hi here is some of mine I start with the middle then i put about 4 around mine are 15 in containers {{gwi:8422}}Anna

goodkamra, have you planted anything yet?

It really depends on the specific annuals you buy. My petunias, for example, are pretty much jammed together with just a couple of inches in between at best. My fancy coleus, with the "fountain" shape and lanced leaves, needs room to show off.

But I think your ten inches apart will look like a really spotty planting with many annuals. In fact, when you're planting a container you typically want to go a bit closer than what the little tag says on the plant.

Linda's idea of the graph paper is a good one. Draw a circle to scale on the grid, and then take it to the garden center with you. When you find a plant you like, look at its recommended spacing and plot it to the circle. Different plants, different plots. Then throw in a few extra to allow for the scootching together you'll probably find you need to do, and you're set!

I wish I'd thought to do this graph paper when I planted my 10' planter this year. Instead, I bought the plants in three trips. Bought a bunch, set them out on the soil and eyeballed how far they'd go. Bought a second bunch and planted everything. Bought the third bunch to fill in where things needed it. I enjoy shopping, but it certainly wasn't very efficient!

Forget taking the graph to the garden center....just figure the plants....
Petunia, annual salvia short zinnias are good at 6 inches.....8 inches is OL for bigger stuff like cleome, the tall zinnia and ageratum...
Better close for a fuller look!
Linda C

Well, you can do it my way. Buy 30 of every plant that catches your eye. Then for good measure put 20 more each in the basket. Then, just-in-case, put another 10 each in the cart too. Once you get home with a truck load of flowers and an empty bank account stuff plants in every conceivable square inch of soil. Be sure to leave 1/4" between flower beds for the truck load you don't know you're bringing home next payday. For containers, oh horror of horrors to be able to see soil!!! At the end of the season stand in the driveway and behold what you have created! HEAVEN! :)