The answer to that is simple. With 3-4 inches of arborist wood chips, it’ll take one year to create one inch of topsoil, because the bottom inch of your layer of wood chips will have broken down by then.
Remember: this will only work if you have the right ratio of green to brown in your wood chips. 20% brown, woody material to 80% green, leafy material is the best.
Wood chips from older branches or tree trunks will skew the carbon to nitrogen ratio way toward carbon. Carbon heavy material is what we call the “brown” stuff, while nitrogen heavy material is what we call the “green” stuff.
If your wood chips are nice and fine, and you have plenty of organic matter in them like leaves and pine needles, then you’ll get more like 2 inches of topsoil out of them after a year. Of course, you’ll need to replace the wood chips that have broken down when the next year comes if that’s the case. You can get away with reapplying wood chips every two years otherwise.
Finally, with wood chips that have many larger pieces, which I wouldn’t particularly recommend because they can be too physically harsh on plants, it’ll take much longer for everything to break down fully. You’ll not get much out of them in the first year, but after they’ve started to break down in your second year you’ll get an inch of top soil out of them each year after that if you keep adding green material on top of it as a nitrogen source. Chicken manure is great for this, if you have a chicken pen.
If there are actually small enough pieces mixed in which can break down in time, it’s possible to get up to half an inch of top soil after the first year you put them down.
This is why it’s nice to have wood chips that are mostly quite fine, but with medium sized pieces and large amounts of organic matter mixed in there too. The smaller the pieces, the quicker they break down, so it’s nice to have the decomposition of your wood chips spread out more evenly to keep your soil protected.