If you want to know just the size of the service, the only two ways to do it is either to look in the service panel and see what the placard says, eg, "120/240 VAC 100-ampere" will tell you the maximum capacity of the panel is 100-amps. It doesn't matter what size the main fuse or circuit breaker is - as long as it's less than the panel rating.
If there is no placard, then the only other way to determine the size of the service is to ask an electrician what size is the meter pan or what size are the service wires coming in to the panel. (There's an easy way to determine this, but since you don't know about it, I'm certainly not going to send you fishing through your electric panel and hoping you don't get fried.)
All that said, there are basically three service sizes: 60-amp, 100-amp and 225-amp. Most houses with circuit breakers that have gas heat and cooking are 100-amp (or 60-amp if they have fuse boxes). Houses with electric stoves, electric heat, or well pumps will usually have 200/225 amp service. You can use your house as a guide.
Doing the math may tell you what you are using and give you an idea of what the minimum service size should be, but you cannot tell from this method because some people intentionally oversize the electrical service.
If there is no placard, then the only other way to determine the size of the service is to ask an electrician what size is the meter pan or what size are the service wires coming in to the panel. (There's an easy way to determine this, but since you don't know about it, I'm certainly not going to send you fishing through your electric panel and hoping you don't get fried.)
All that said, there are basically three service sizes: 60-amp, 100-amp and 225-amp. Most houses with circuit breakers that have gas heat and cooking are 100-amp (or 60-amp if they have fuse boxes). Houses with electric stoves, electric heat, or well pumps will usually have 200/225 amp service. You can use your house as a guide.
Doing the math may tell you what you are using and give you an idea of what the minimum service size should be, but you cannot tell from this method because some people intentionally oversize the electrical service.