^ This.
Also, it depends on how high you plan on mounting the fixtures. My shop is 40x35 with 14' wall height and 4:12 pitch roof that is about 21' at center. I currently have (6) 4-bulb 4-foot LED fixtures, with about 10000 lumens per fixture and internal foil reflectors. Hung them with "aircraft" cable so I could adjust height. I started at 14 feet, measured lux at bench height and it didn't seem like enough, lowered them to 12.5' and it made quite a suprising difference. I still need to add 3 more around the perimeter where I have benches, but I could get by with what I have and add local lighting.