Here is just a bit more to expand on the great info and explanation that 79pmooney provided on "gear number" and how to calculate it.
IF YOU TAKE THAT "Gear Number" and multiply it by pi .................that will give you the NUMBER IN INCHES you travel with each revolution of the pedals.
REMEMBER THAT pi is 3.14
.....so "GEAR NUMBER" X 3.14 = amount in INCHES that your bicycle travels with each revolution of the pedals
Then take that RESULT IN INCHES and divide by TWELVE to convert into FEET which may will be more meaningful and easier to visualize.
(*****alternatively you could convert that RESULT in inches into METERS, YARDS or whatever measurement makes you the happiest!*****)
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---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- To Recap and Summarize what 79pmooney briefly but expertly explained earlier:
TEETH ON FRONT SPROCKET divided by TEETH ON REAR
take that and MULTIPLY it by 27 or 26 depending on the size of your bicycle's wheel (USE 27 for 630mm(27)... and for 622mm(700C)....)
(USE 26 for the 597mm schwinn tire, the 590mm common 26 x 1 3/8 tire, the 650 a, 650b, 650c tires, the old 584mm, and 559mm tires....)
Example: 45 teeth on front sprocket ........ divided by 15 teeth on rear = 3
3 X 27 = 81 gear number
IF YOU WANT TO KNOW HOW FAR YOU WILL TRAVEL WITH EACH REVOLUTION OF THE PEDALS,
Take that 81 gear number and multiply it by pi and that will give you the total in inches that you travel with each pedal revolution.
So you would multiply 81 X pi ...................which would be 81 X 3.14 since pi is 3.14 when limited to just two decimal places....
Even Jethro Bodine can do this simple calculation.
I know you probably think it is too simple to be useful but as 79pmooney pointed out, this has been around for ages and it is very useful.
FIFTY YEARS AGO,SCHWINN and other manufacturers routinely stated the "gear number" for each and the overall wide range for ten speeds and five speed bicycles.
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It is important that you select the appropriate (27) or (26) to be your wheel size in the simple calculation.
Why? Well I hope this ancient example is okay, since I am an ancient Schwinn rider and collector.........
The ancient early seventies to late seventies FIVE SPEED Collegiates and FIVE SPEED Suburbans have the exact same freewheel(32-26-21-17-14) and 46 teeth front.
The SUBURBAN has 27 x 1 1/4 630mm wheels --and-- the COLLEGIATE has 26 x 1 3/8 those 597mm wheels.
Well excluding the math computation.................IF YOU WERE TO COMPARE the 46 teeth Front and 17 teeth REAR combination (which is 4th gear on these ancient schwinns)
Well that 27 inch wheeled SUBURBAN would have a 73 gear number for that 46 Front and 17 Rear .....and travel a distance of approx 19 feet with each crank revolution.......................................that 26 inch COLLEGIATE would have a 70 gear number for that 46 Front and 17 Rear and travel a distance of approx 18 feet with each crank revolution...................so what you already knew but probably didn't much consider and that is that yes the wheel size does influence the overall gearing, and as you can see that having identical front and rear sprockets on different bicycles can't be considered exactly the same in overall gear ratio UNLESS the wheel diameter is indeed the same between both bicycles.................or more or less the same where the slight variance or difference is immaterial and not meaningful.
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here is another speed at cadence chart that you can see at the same bikecalcDOTcom site that Ga Dude posted earlier.
https://www.bikecalc.com/speed_at_cadence