How big is a 10 gallon turtle tank?

The proper rule of thumb is 10 gallons for every inch of Aquatic turtle you have. So if your three turtles each measure 4 inches long, for example, you need to have AT LEAST a 120 gallon tank.

No Tank is Really Going to be Large EnoughFor a group of turtles, no aquarium is ever really going to be large enough. The post above provides an Excellent guideline for how much swimming space to provide your turtles - but you must also allow for basking space as well. Your best bet is to look into a preformed pond (which are available at most home improvement stores). When set up properly they provide a more natural habitat (less stressful for your turtles), and are much easier to clean, light, and heat... they are also far less expensive - allowing you to spend your money on fixing them up - rather than providing the bear minimum. :)

That is not true you need maybe about a 30-40 gallon tank. :)