How Much Deck Stain Do I Need?
The coverage on a stain label is usually ideal; real coverage drops with wood porosity, old coating, spray/roller method and waste. Calculate the paintable area, then add 10–20% so you do not run short and create a color mismatch.
Calculate the area
Deck area = length times width; railings/steps are separate, not just the floor.
New or rough wood absorbs more; coverage can drop 20–30%.
Old coating needs compatible cleaning/sanding or the new stain will not bond.
How much to buy
Use label coverage times coats, then add 10–20%.
Buy the same batch/lot to avoid color differences.
Test a small area and check the color after it dries.
FAQ
How many square feet per gallon?
Check the label; commonly 200–350 sq ft per gallon, use the low end for rough wood.
Do I need two coats?
Most transparent/semi-transparent stains recommend two coats; solid stains may need one, follow the label.
Spray or roll?
Spraying is faster but wastes more; rolling/brushing uses less, and back-brush after spraying.