Tomato seeds can be started in small pots of damp seed starting soil, damp potting soil, or in moistened peat pellets. In each container you will be planting two tomato seeds. This will help ensure that each container will have a tomato seedling, in case some of the tomato seeds do not germinate. The tomato seeds should be planted about three times deeper than the size of the seed. This will be about 1/8 to 1/4 of an inch (3-6 mm.), depending on the tomato variety that you have chosen to grow.
Read more at Gardening Know How: Planting Tomato Seeds – How To Start Tomato Plants From Seed