Can someone tell me how to find out what the amp rating of a service to a house is . The fuse box is old with edison base fuses, but the weather head and pipe to the meter cradel looks newer want to change to beaker panel
Not sure what size

I would worry less about what you have, than what you need. A 100 amp used to be standard, but I think 200 amp is more common now. I am not real familiar with newer code, but I think you can put in a 200 amp box. It may take some other upgrades, but it should be adequate for even a large residence. Many people are replacing 100 amp boxes with 200 amp ones. May as well start with the 200 amp. Once installed, it can stay as you make other upgrades. Do some looking at what is available and prices. See what other answers you get.

I like the way Labman put that answer. Just because the outside may look new does not mean you could simply replace the panel.

The main fuses in the panel will give an indiaction of size service you have, and most likely the wire and conduit is all rated that size.
Now I don't want to assume that you only have the typical 60 amp service installed by Moses. You can certainly have either a 100 amp or even a 200 amp service, and using all fuses. Yes back then some 100 a and 200a services were installed.
Take a look at your main fuses, and get back with that info, along with any other details you can offer, such as the quantity of edison fuses, all the sizes of these fuses, a list of circuits and appliances.

We can go from there.

OK I will look at that I think its typical 8 fuses 60 amp main fuses 250 amps buss style. They have ac want to ad a hot tub 240 vac 40 amp
100 amp will be fine . Do not want to change meter creadle and or weather head if not needed. I was told round meter 60 amp square 100 amdp and rectangular 200 amp service any truth to this ? Would someone upgrade the service and not the panel?

I don't know about the newer ones, but my 1970 100 amp box is wired to the meter base. If you can buy a 200 box with 40 slots, meant to be wired to the meter, that would be the best thing I think. Not the cheapest.

I wonder if I can buy a 40 slot, 200 amp box with a built in double throw switch so I can legally wire my generator into my house wiring?

When it comes to ratings of electrical equipment, you cannot rely on age,looks,or shape. You must look at each piece, meter, wire,conduit, and know exactly what each is, just like you did with the fuses.

If the meter is only 60 amp, and you change the panel to 100 or 200 amp, all you have is a cadillac body with a lawnmower engine. You haven't accopmlished anything except expend money and labor for nothing. ANd the worst is if you actually install a 100 amp panel with a 100 amp breaker on a 60 amp service, hope you live close to the fire dept. because it will burn.

No, I am sure someone did not upgrade the conduit riser and the meter socket to 100 amp and leave the 60 amp panel.

How are you sure a 100 amp service is enough? Adding a 40 amp hot tub load uses 50 % of the 100 amp capacity, ahh new math you think, or I am using my calculator backwards. No, any service must not be loaded more than 80% of it's capacity, therefore, with a 40 amp hot tub load, you will only have 40 amps left for the entire remaining home, including the AC, hot water, range,DW, lights, kitchen appliances.

Trust me, you install a 100 amp service without having the appropriate calculations done, you can expect big problems, waste money, and possibly loose your home. Give me all the appliance in the home, and the total living space square footage, and I can run the calcs. I will not guess at this. If you do, I wish you luck.