Feet do not test concrete
A person walking is about the lightest thing anyone ever puts on a slab. Four inches of concrete on a base that does not move will take that traffic for as long as the house stands, and no amount of extra depth improves on it. If a walk on your property is broken up, look at what is under it before you assume it was poured thin. Nearly every broken walk we get called out to look at is a base problem or a joint problem being blamed on thickness.
Where thickness does become the answer is the moment a wheel is involved. A tire concentrates a vehicle into four small contact patches, and a narrow slab has very little concrete on either side of that patch to help carry it. That is a different question from foot traffic, and it gets a different section.
The stretch where tires cross it
Walk your own property and find the places a wheel actually crosses the concrete. The apron where the walk meets the driveway. The corner a delivery truck cuts when it swings in. The line the mower takes every week. A path along the side of a shop that the tractor rides over to get to the back. Those places are the whole of the thickness conversation on a walk.
Where a vehicle crosses, we thicken that section and reinforce it, and we deepen the edge rather than leaving a feather of concrete for a tire to break off. A mower is not much, and standard section handles that. A loaded pickup crossing a four foot walk is a real load, and it wants the treatment a driveway gets.
The important part is telling us at the estimate. Once the boards are set and the concrete is ordered, the section is what it is. Nobody thickens a walk after the fact for less than the cost of pouring it again.
Width does more for you than depth ever will
A three foot walk is plenty for a side path between the driveway and a back door, where nobody is going two abreast anyway. At four feet, two people fit alongside each other, and that is also the width where a front walk stops looking tacked on and starts looking like it came with the house. If there is a fixed amount of money for the job, that fourth foot buys you something you use every single day. A fifth inch of depth buys you concrete nobody will ever see or feel.
The same is true of the run. A walk that goes where people already cut across the grass is a walk that gets used, and one that takes a scenic route gets a dirt track worn in beside it. Straight runs also form fast and finish clean, while every curve is bent and staked by hand and shows up on the estimate. Simple and wide beats fancy and deep.
A narrow slab feels a soft spot sooner than a wide one
There is one honest reason to care about what is under a walk more than you would under a bigger slab. A ribbon of concrete three or four feet across has very little material to bridge a soft place, so ground movement shows in a walk earlier than it shows in a patio poured over the same dirt. Native ground here is red clay, which holds water, swells and moves through every freeze.
The fix for that is not depth. It is crusher run stone compacted in place so water has somewhere to go, and it is keeping downspouts and roof runoff from soaking the ground alongside the walk. Frost heave lifts a slab because there is water in the base to freeze. Take the water out of the equation and the section you have is enough.
Joints do the rest. Walks get jointed on a spacing that suits the slab so shrinkage lands in a cut line instead of wandering, and where the walk meets a stoop, a foundation or a driveway, we isolate it so two pieces of concrete that move at different rates are not fighting each other.
The rate does not drop because the slab is thin
Sidewalk work runs $10 to $15 per square foot installed. People are surprised that a walk carries a higher band than a driveway at $8 to $12 when it is the smaller, thinner pour, and the reason is that flatwork pricing follows forming and finishing labor rather than the volume of concrete in the ground. A narrow ribbon is almost all edge.
That is worth knowing before you ask whether a thinner walk would be cheaper. It would not be, by any amount worth having. Steps do not get a square foot rate at all. A flight is quoted on its own line, because what you are buying there is form work and hand finishing rather than area.
We measure on site, walk the route with you, and hand you a free written estimate that spells out the width, the section, and where it gets thickened, usually within a day or two. The workmanship warranty is in writing with the exact terms confirmed on that estimate.