There no positive way, but you can get an idea from the Model number. It will be five or six digits. The last four describe carb, bearings, starter, etc. The first one or two are the cubic inches of the engine. Current decals are a torque ratings. You can also go to Briggs at the attached link with the model number and see.
were can i find a wiring diagram for a 18 hp briggs and stratton engine
At briggsandstratton.com
Click the link and find your engine for the exact capacity.
How do I change points to electronic ignition on a 5 hp briggs & stratton small engine?
Roughly 16.5 HP
0.030 is the gap for briggs and stratton 4.5 hp mower
Click the link and find your engine for the capacity.
Timing is off ...
.030
Briggs & Stratton part # 491056 NAPA filter # 1348
44oz
.010mmType your answer here...