I plan to use full dimensional 1"x8"x 8' long- Hemlock planks for the interior of a shed floor. I'm planning on using 1.5" x 5.6" x 12' pressure treated joists, posted at 6' intervals to carry them. The floor size is 8' x 18' so the planks would go outside edge to outside edge

Can I do 32" spacing of the joists? 24" spacing?


|<------------------------------------ 8' ------------------------------->|
| |
==========================================
II II II II 32" ctrs

OR

==========================================
II II II II II 24" ctrs

A question for you, what are you going to store on this floor?

Anything with weight will make a 1" floor sag in time,especially if you space the joists 32" apart.

I would think of:
1) How long do you want the floor to last before repairing it?

2) The weight(load) on the floor?

3) Moisture under the shed?

4)How much is a few more 2Xs going to really cost versus the maintaining of this shed?

Going with 17" ctrs and the 1x8's XpX X X X X XpX x's are 2x6 p's are 4x4 posts.

This thing keep taking out most of my spaces; XpX_____X_____X_____X_____X_____XpX

You need 16" on center. only time you use 24" center is for an engineered roof, as for a floor with just a few joist in it, will bounce and sage very quickly. The treated joist aren't that expensive, do yourself a favor and just do it right the first time, you'll be sorry if you don't, when you realize you need more support its going to be much more of a job than it is now. You shouldn't need more than 13 of them, $130 buck give or take, short cuts will always come back to bit you, avoid this one