I ride a Trek Verve 2 with Bontrager H5 700X45c tires. I do casual but extensive riding, only going about 10mph but over 100 miles a week. It is about 70% bike path, 20% suburban paved road and 10% gravel and simple, low tech single track.

I am looking at replacement tires and do not need more grip or more speed or more comfort. I am happy to pay for a premium tire and if I were to pay for more of anything it would be more puncture resistance. Despite the low usage off road, I very much value having the good grip when I am on a trail and am willing to give up speed and smoothness on pavement for that grip.

What I have works fine but it is no longer available. While looking online I am not seeing anything in 700X45c size and do not know how much larger or smaller I can go. My rims have 20mm inner width and 26mm external width.

Is there some formula for determining what size range I can consider?

Are there any recommendations for good all-around tires for a hybrid that might fit my rims?

Gravel Kings SS+ are pretty much good all around tire with great puncture protection.

Agree, it's hard to beat Gravel kings and you can likely find a tread pattern that suits you. 42mm width is widely available, you won't notice a difference. If that's a motorized bike you might consider buying three tires at a time. The rear can take a beating from all the power and acceleration on hills.

Thanks guys, those look good, and the SS+ comes in 700X45.

Check out the table in red and green for which tire size (width) is safe to use. Note that there is a statement at the bottom of the chart that the recommendations are conservative when it comes to safety. https://www.sheldonbrown.com/tire-sizing.html