Depends on if you're looking at the wheel or if you're looking at the pedals.
1st gear, the one where pedalling is easiest, is the biggest sprocket at the rear, and the smallest chainwheel at the front.
1st gear is the gear where you can pedal with the least resistance. For a bicycle with external gears the chain should be on a big sprocket at the back and a small chainwheel at the front.
First gear on a bicycle with external/derailer gears is with the chain on the smallest chainwheel(by the pedals) and the biggest sprocket(by the rear wheel).
Larrge at the front and small at the rear
On a bike there's one(or more) front sprocket(s) by the pedals connected by a chain to one(or more) rear sprocket(s) by the rear wheel. As the wheel isn't driven directly by the pedals, and there's usually a difference in size between the front & rear sprocket this constitutes a gear.
It depends on whether you are talking about the front sprocket (the one at the pedals, called a chainring) or the sprocket at the rear derailleur. The lowest gear at the front is the smallest sprocket/chainring. The lowest gear at the rear is the largest sprocket. So if you combine the smallest sprocket at the front with the largest sprocket in the rear you have the lowest gear available on your bike.
Chain is on the smallest sprocket on the crank and on the largest sprocket on the rear wheel
the smallest sprocket is the highest gear.
First gear on a bicycle with external/derailer gears is with the chain on the smallest chainwheel(by the pedals) and the biggest sprocket(by the rear wheel). Answer These terms are often confused, probably because bicycles pre-date automobile transmissions. For anyone who has driven a car, "first gear" is normally associated with the gear that has the most acceleration. For most multi-geared bicycles, the combination of the smallest cog on the front chainring and largest cog on the rear cassette gives the greatest acceleration or power. Using an automotive analogy, this is your first gear. "Big gear" and "little gear" is a holdover from the Penny Farthing "boneshaker" bicycle in which more speed was gained from each turn of the pedals by making the front wheel larger (ow!). It now refers to the measure of how much chain passes through the gears for each turn of the pedals. A big gear is one that is normally associated with a combination of gears using the large chain ring on the front and a small gear on the rear cassette. A little gear uses a small chain ring on the front and a large sprocket on the rear cassette.
Bicycle gears are measured in inches. The formula is 27 (Size of wheel.) divide by number of teeth on rear sprocket. Multiplied by the number of teeth on chainwheel. Example 27 divide by 18, times 50, equals 75.0 inch gear.
In bikes it's more common to count teeth rather than sprocket diameters. But if the smaller wheel is half the size it'll turn twice as many times.
The sprocket on the nose of the crankshaft that drives the cam sprocket.