Is there an aftermarket gas cap fuel gauge for Honda motorcycles?

Is there an aftermarket gas cap fuel gauge for Honda motorcycles? - 1

I doubt it, fuel gauges are quite intricate mechanisms, attaching one to a fuel cap would mean pulling it out every time it was filled up and that would lead to damage.

I just use a trip odometer to remind me when I'm low on fuel or rely on the reserve getting me to the next filling station.

Same as Tim D. If you want a modern bike with a capacitive fuel quantity sensor, buy a a modern bike with a capacitive fuel quantity sensor. http://omnicomm-online.com/products/sensors/

Back in the 70s, some accessory manufacturer made replacement gas caps that had built in fuel guages. They had a little float that hung down in the fuel tank. They were not all that accurate and they stopped making them.

I'm not aware of any either. I always set my trip meter every time I fill up. That will generally tell me when I'm getting close. And when my bike starts missing, I know it's time to switch over to reserve (and start looking for a filling station).

Year? Make? Model?
What bike are you inquiring about?

They were around & not much use because most bikes have a saddle tank - ie it sits over the top frame & is lower at the sides. This makes it almost impossible to make a gauge that can give any sort of reasonably accurate reading. As others have posted reset your trip meter when you fill up &take note of when you need to switch to reserve. Typical range would be 100 to 250 miles (150 400 km) depending on bike & riding conditions. You've typically got about 15 to 20% reserve in the tank ie 10 to 50 miles. Fill up well before you run out. It is a bad idea t orun the fuel too low as the gunge sitting in the bottom of the tank will end up in the carbies requiring a strip & clean.
ie plan your refueling & trips so you're filling up about at the point of hitting the reserve

When I rode Hondas, I became used to the factory supplied eyeball and brain.

Good thing, the new-fangled doodad on the HD takes forever to find it's level and the low fuel light will light at 1/2 tank (2.5gal+ a hair) on the jiffy stand.

Seeing as Honda has made bikes for over 50 years, there's no way to answer.

Most bikes have a tunnel in the tank so it fits over the frame and a gas cap guage would not work.

Why can't you just unscrew the cap and LOOK in the tank?

Tap the side of the tank before you start it. Find where the sound changes-that's how much fuel you have. As in all things motorcycle, experience is valuable. Make sure you live long enough to get some.