How much surface can I cover with one gallon of mixed epoxy?

The term 'mixed epoxy' refers to the amount of resin and hardener combined to equal 1 gallon.

Wetting out fiberglass and other composite fabrics:

The estimates below indicate only how much mixed epoxy resin and hardener is needed to wet out a specific fabric type; it doesn't account for mixed epoxy applied to a surface before wetting out the epoxy, or epoxy applied between composite fabric layers. Taking this information into consideration, by fabric type, one gallon of mixed epoxy will wet out approximately:

• 4 oz. fiberglass cloth - 37.5 sq. yds.
• 6 oz. fiberglass cloth - 25 sq. yds.
• 10 oz. fiberglass cloth - 5 sq. yds.
• 1708 biaxial fiberglass cloth with mat backing (23.75 oz. per square yard) - 6.4 sq. yds.
• Fiberglass chopped strand mat (CSM) - 5 sq. yds.
• 18 oz. fiberglass woven roving - 4.5 sq. yds.
• 24 oz. fiberglass woven roving - 3.5 sq. yds. 

Sealing, coating, or pouring a slab

The following yields don't account for wasted product, which could be 15-20%, due to drips and material left in the mixing cup, on brushes, spreaders, or other tools.

• 6.4 sq. ft at a thickness of 1/4 inch
• 12.8 sq. ft. at a thickness of 1/8 inch
• 25.6 sq. ft. at a thickness of 1/16 inch