According to Microsoft, if you have the following Office 365 subscriptions:
Office 365 Home
Office 365 Personal
Office 365 University
Office 365 Home Military Appreciation Edition
Office 365 Home Trial
You’ll be able install Office 365 on all your devices and be signed in to five at the same time―that means you can use Office no matter where you are or what device you’re on. This includes any combination of PCs, Macs, tablets, and phones.
And if your running Office 365 for business:
Office 365 Business, Business Premium and ProPlus subscribers can install Office on up to 5 PCs or Macs, 5 tablets, and 5 smartphones. You can count hybrid Windows devices, such as the Microsoft Surface Pro, as either a PC or a tablet.
Nice to see Microsoft being flexible when it comes to device limits.
Related reading: Microsoft to increase device limits for Office 365 consumer subscription users