Its value in different countries is different as per the trade terms. In North America and Canada, 100 pounds is equivalent to 1 Hundredweight (also known as small hundredweight, equal to 45.359237 kg) and similarly, in UK, its value is 112 pounds is equal to 1 Hundredweight (also known as long hundredweight), also equal to 50.802345 kg.
The meaning is same as both of them have equal number of units in a ton (Same convention). Singular and plural forms of hundredweight are the same. Mixed measures are not allowed in SI system.
If we see now, its usage has declined now, owing to its specifications in different units but still imperial system is used where old traditional things are being used such as bells in church, etc.