As part of today's slate of errands, I noticed that the gas gauge in the car was finally a bit below a quarter of a tank, so I went to the gas station. Because I'm one of those guys who inherited the habit of logging fill ups in a little book in the glove compartment, I can see immediately how long it has been since the last one. In this case, without even getting to full bike commuting, it had been 23 days.
I'm not the best example of your potential savings, because I don't drive anywhere except to work and on necessary errands, like the grocery store. During the pandemic I have avoided combining grocery shopping with the drive home from work on days that I'm in the car, because the incidence of mouth breathers is much higher then. I don't need the aggravation.
My commute by car is about 28 1/2 miles round trip. By bike it's just over 30, because of route variations I use to avoid an unpleasant section of road. The direct route is okay on the ride in, because gravity is with me, and we're all going into town, where motorists have no choice but to slow down. No good choice, anyway. I have envisioned the Grand Prix de Wolfeboro, where we have a full-on, closed course motor race around town. In addition to the Formula One category there can be a "run whatcha brung" race for the locals. That might have to be broken out into further subcategories for rat rods, drift cars, soccer moms, monster trucks, and midlife crisis dudes. So far I have not lined up any sponsors. The people you see practicing are doing it on their own.
Once the weather gets more reliably mild, I routinely go a month without filling the gas tank, and that includes a few optional trips to nearby trail heads or boat launching sites. Your results may vary.
And now for the standard disclaimers: Bike commuting is not for everyone. Many people are unable to do it because of distances they have to cover, loads they have to carry, lack of changing facilities at work, and a host of other insurmountable obstacles. But don't let your privileged status discourage you if you realize that you could commute by bike, but don't, in sympathy with the true prisoners of motorized society. Every bike commuter is saving a parking space, and helping to bring gas prices down by reducing demand.You may not think your individual efforts will have an impact on the thick hide and monstrous body of the oil industry, but add yourself to the unseen multitude across the country who are doing the same thing. The more the better.