- Series 3 38mm — Height: 38.6mm / Width: 33.3mm / Depth: 11.4mm
- Series 4 40mm — Height: 40mm / Width: 34mm / Depth: 10.7mm
- Series 3 42mm — Height: 42.5mm / Width: 36.4mm / Depth: 11.4mm
- Series 4 44mm — Height: 44mm / Width: 38mm / Depth: 10.7mm
Apple says all old bands are compatible across the new generation of watches, which is great.