Concrete thickness will vary depending on the soil the driveway is being installed on as well as the industry standards in your area.
Here, in Denver Colorado, we have two types of soils we install concrete on. First, on the front range, the soils tend to be expansive soils so most contractors usually install 3" to 6" inches of structural base and then pour 4" to 6" of concrete. In the mountains, however, the soil is decomposed granite which is almost identical to that of a structural road base, you couldn’t ask for a better sub-grade, so most contractors don’t install base but pour 4" of concrete thickness.
Now, usually a residential driveway has nothing more than everyday passenger vehicles driving on them, but if you have delivery trucks, trash collecting trucks or any other large commercial vehicles that will be driving on your driveway on a regular basis make sure you let the contractor you plan on hiring know this important information. If it's at all possible, you really should try and eliminate the need for these vehicles using your driveway. These heavy vehicles can cause severe damage over time regardless of the concrete thickness.
Now, the only way to guarantee the right concrete thickness for your soil type, is to hire a soils engineer to evaluate your soil and come up with a concrete pavement design for you. However, that can multiply the price of a concrete driveway by two to three times. Even then there's still no guarantee it wont crack. Really, the reputable contractors in your area will know what the proper thickness the concrete should be for your driveway.
Installing a concrete driveway too thin is actually a common rip off practice by the "fly by night" unethical contractors.
Be sure to watch or read our series “The Most Common Ways Concrete Installation Contractors Rip Us Off and How To Avoid Them” before you hire a concrete contractor. This will give you the information you'll need to pick out a good quality contractor.
If you'd rather, let us do the hard work for you and request a concrete installation estimate from one of our Trusted Concrete Installation Contractors!