The Classic MX Modular Armband fits the iPhone 8 Plus with no case or a thin case and is the best armband choice if you want the least amount of bulk on your arm while running or working out.
The Classic MX Modular iPhone 8 Plus Armband fits cases up to 162 x 83 x 10 mm.
If your case is thick and you prefer to keep the case on during your workouts, we recommend the Entropy E8 Armband for iPhone 8 Plus.
Strap Size Arm Size (upper arm circumference)
Small 7 - 9.5 inches (20 - 25 cm) - For THIN arms or wrists only
Medium 10 - 14 inches (25 - 36 cm) - Fits most arms/most common size
Large 13 - 18 inches (33 - 46 cm) - Fits large arms or over clothing
Extender + 4 inches (10 cm)