It's amazing that Federer has won the same amount of single titles on grass as Nadal on hard court. Grass season only lasted 1 month and the players only participated 2 events per year, and there's no MS1000 either. OTOH, most tournaments are on hard court that spread across the world and are available throughout the year. Hard court is the common surface that all players play on the most from every level(ATP250/500/1000, WTF, Slams).
Breakdown Federer's 19 grass titles and Nadal 19 hard court titles:
Number of slams
Federer - 8(Wimbledon)
Nadal - 4(3 USO, AO)
ATP250/500/1000
Federer - 11
Nadal - 14
Olympics
Nadal - 1
Federer - 0
Record in the finals
Federer - 19-7(73%)
Nadal - 19-26(42%)
Breakdown Federer's 19 grass titles and Nadal 19 hard court titles:
Number of slams
Federer - 8(Wimbledon)
Nadal - 4(3 USO, AO)
ATP250/500/1000
Federer - 11
Nadal - 14
Olympics
Nadal - 1
Federer - 0
Record in the finals
Federer - 19-7(73%)
Nadal - 19-26(42%)