>>827208wikipedia has some good figures:
JR East
System length
Total 7,526.8 km (4,676.9 mi)
Double track 3,668 km (2,279 mi) (49%)
Electrified 5,512.7 km (3,425.4 mi) (73.2%)
High-speed 1,052.9 km (654.2 mi) (14.0%)
JR West
System length
Total 5,012.7 km (3,114.7 mi)
Double track 2,253.2 km (1,400.1 mi) (44.9%)
Electrified 3,385.7 km (2,103.8 mi) (67.5%)
High-speed 644.0 km (400.2 mi) (12.8%)