A simple coin can check your tread depth, but the results—unless you know exactly what you're doing—can certainly vary. And the coin test is not meant to replace real measurements. Invest that loose change into a product that guarantees good results.
The Dill® Digital Tread Depth Gauge is only $19, and can be used to measure brake shoe and pad wear as well. Tread depth is displayed on an easy-to-read digital screen, and readings can be taken quickly and accurately whenever and wherever.
Click here to see all the air and tread depth gauges in Tire Rack's inventory of aftermarket accessories.