Thanks
@Spirit Reborn,
I guess I determine that with the temps outside more than plant size. If its staying above 50 F at night, you can go ahead and transplant. First you need to "harden them off", take them outside for a couple hours of sun, somewhere out of the wind, the first day, then 5 or 6 hours the next day, about 5 days of this will toughen them up.
When transplanting tomatoes, i dig like an elongated hole and lay the tomato plant kind of horizontal or at an upward angle. Depending on how tall the plant is, leave a few branches and leaves above the dirt and cover the rest. The stalk thats under the dirt will then also sprout roots and be able to supply the plant with more water and nutrients than just planting the root ball.
Heres more info,
How to Grow Your Own Tomatoes, Part 2: Transplanting - Modern Farmer
God bless and happy gardening