With an online estimator I figured that an 18'x9'x4" slab is 54 cubic feet of concrete, or exactly 2
yards.

Is 4" thick enough for a driveway and how much is 2 yards of concrete, delivered(about)?

Do I need to allow for extra concrete? Can I go to 3" and make a bigger slab?

  If I were building a driveway today , I WOULD NOT be satisfied with a 4 inch thickness .
 You never know what kind of vehicle will end up driving on it . Delivery truck , etc.
Use mesh and rebar as well .  No idea of the cost.

Quoted:   If I were building a driveway today , I WOULD NOT be satisfied with a 4 inch thickness .  You never know what kind of vehicle will end up driving on it . Delivery truck , etc. Use mesh and rebar as well .  No idea of the cost.

The only thing in my driveway will be a corvette.

As I read your post again , you say slab AND driveway . Which is it ?

4" is typical.  However the thicker the better.  The use of mesh and rebar is common, however, not necessary for your application.  Need to pay attention to your contraction joint spacing(8' to 12' for 4" thickness, better results with tighter spacing to control cracking) and depth of joints(1/3 of the slab thickness).  All this set aside, get a good finisher, you can have all the design principles covered and a finisher can ruin the entire thing.  

Good luck.

I have a good finisher online for the job who will work for beer!

How much is a yard of concrete?

Quoted: Quoted:   If I were building a driveway today , I WOULD NOT be satisfied with a 4 inch thickness .  You never know what kind of vehicle will end up driving on it . Delivery truck , etc. Use mesh and rebar as well .  No idea of the cost. The only thing in my driveway will be a corvette.

and when the corvette is not there, you don't know who will be using your driveway for turning around, etc...I hate that shit...

$70/yard here.  I'd hate to pay the delivery charge to FL though.

I have 5.5" with glass fiber, and park a semi truck on it. Labor that works for beer, USUALLY looks like it was done by a drunk...

use mesh, concrete with fiber, and make sure you have a good base to pour on.

I had a pour 21 foot wide and over 120 feet long, along with additional flags and patio.  3.5-4" is typical with 6 sack mix or pump mix with wire or rebar.  I had several cars on it, including a 1 ton crew cab pickup and a 10000 pound+ trailer.  Trust me, it is enough.  No cracks.

Quoted: Around here you just take the exact dimensions to the concrete plant and they calculate the cost from there (extra on Sat. morning, due to demand).  They send a truck full and he pours enough to fill your forms.  You do not need to calculate the exact amount you need.

What the online estimator will NOT tell you is what the minum yardage is for free delivery or what a delivery charge may be.  3 yards is a typical minimum order.

6" thick is preferred. 3" is OK for sidewalks, patio's but not for parking 2 ton vehicles.

Concrete's enemy is water. Water will make a thin slab float and crack.

Also, I would use either #3 rebar or welded wire fabric or your going to get cracks in the slab, especially the edges due to the vehicles weight. Make sure you put a couple of inches of sand bedding in the excavation for the slab to sit on, this will reduce settling and cracking also.

Be sure to install a wooden expansion joint down the middle and at the start of the return to the street and against any existing concrete to allow it to expand and contract due to temperature changes.

Quoted: I have 5.5" with glass fiber, and park a semi truck on it. Labor that works for beer, USUALLY looks like it was done by a drunk...

He is a drunk but he does stellar work. He's poured all the slabs around here and he's a very hard worker.

The base will be sand unless I put in some gravel first.

Minimum order shouldnt be a problem, I'll work around 3 yds+.

How much is the mesh and is fiber concrete expensive?

Get more concrete than you need.  Imagine have the whole slab poured only to fall short 1 foot.  If you never done a job like this, I would suggest that you hire a contractor to do it.  It's not like you're going to be doing 5 of them.  Just one, pay for it and get a nice one.  Figuring out how to screed, float and finish (or screaming at your freinds) while the concrete is cooking off and setting is not something you want to do.  It is far more costly to redo it than to just pay to have it done right.  I would guess that it would cost you about $2,000 to get it done.

Mesh comes in rolls with different lengths and mesh sizes. I imagine anywhere from $50 to $200 depending on the roll width and length.

They start at 18" wide and go up to 72" wide and length from 100 feet to 165 feet per roll depending on gauge.

Heavy gauge is 11 down to a light gauge of 23. Also the mesh configurations vary depending on the dimension between the openings.

Mesh will do no good unless it is placed on plastic chairs or spacers that get it up off the sand and into the middle of the slab. Mesh is hard to work with, cut and install. If I were you I might look hard at the fiber mix, unless you have a someone who knows how to properly install the mesh.

http://www.nrmca.org/aboutconcrete/cips/

Link from National Ready Mix Association.  Links are to various topics on concrete.  I couldn't find a link about parking lots.  However, 4" is good for up to shopping center type volume traffic, assuming you are on a solid subgrade.  Two things concrete is going to do is crack and get hard.  You can't stop either one.  You can retard it getting hard, but it will crack.  That is the purpose for the joints, to make it crack where you want it to.  

If you do a detailed design, you very rarely come out with a thickness greater than 9".  The interstates are typically built on 9" slabs.  No rebar, no mesh, no fiber.  The joints do have smooth dowels for to allow for expansion while maintaining support at the joint.  Fiber is common also, some people don't like the finish.  Any steel takes the place of where concrete should be for slabs.  Wire mesh usually never winds up in the place it should be in to have any effect anyway.  Rebar constrains the conrete and induces cracking in some cases.  

There are plenty of more issues, if it was mine:

5"
joints at 8' invervals
expansion at fixed structures and 40 foot intervals
no mesh, wire, rebar
solid subgrade
get a good finisher

With todays market, I doubt it will be done for less than $2500 and probably closer to $3K.  I also bet that if you call 10 folks for estimates, 2 will show up.  

Don't let the guy with shiny boots and no tape measure do the job, and kick him in the ass as he is leaving.

(btdt)

Having done this a few times, even the pros fuck up on the concrete estimate.  They are good at concrete, not math.

And as far as beer, it is pain killer for the finisher.  Finishing concrete is a cast iron bitch!!

Capt Pooby--you say sand is the base--are we talking Myrtle Beach-type sand? If the sand you want to pour concrete upon is residual, you might want to have that checked to see if it'll support a minimal bearing pressure--if it has been used as fill, you might be all right-if it has been compacted properly and the sand is not too wet, or too dry,  or really a variety of other factors..you might be all right.....Sand can be (real) tricky to work with to insure it'll bear a minimum 2000-3000 psf pressure.

I just don't want to see later that the subgrade (or below that) was too loose to work with and see that over (a relatively short period of) time the slab will crack or even worse, settle and break (up).

If you have any queations, IM me-I just worked a project in S.C. where Myrtle Beach sand was the entire base, and a community center was built, with a 3,000 psf bearing pressure requirement. And the builder was really sweating on building upon sand--considering residual (existing) sand at that particular location was bad at about 9' deep--so the area was undercut that deep, and backfilled and compacted to be able to build upon.

Capt Pooby,

You've got some great advice so far, about the only thing I can add is cost varies greatly. Around here we are  paying $94.00 per yard, thats without cold weather provisions(hot water mix, chemical hardeners.....). Apparently there is still a shortage from the hurricanes, how that effects us I have know idea. One thing you might look into is Xypex http://www.xypex.com/applications/admix.html
its supposed to make concrete last alot longer, alot of the local architects are speccing it.

Well, Florida is made entirely of sand, so thats what the base will be. My concrete guy has laid several slabs here at the DZ and not one has cracked and they're all nice and white so I feel good about that.

I'm trying to get an idea of what this will cost me.