I am upgrading my laundry room and my bathroom in my basement. I was going to run 8/3 wire with ground to my electric dryer and then I was going to run 10/3 wire to my washer outlet. From the washer I wanted to run 12/ 3 wire to my GFI bathroom outlet and from this outlet 12/3 wire to two other outlets, 3 can lights and a bathroom fan. Can I do this or should I just run a separate 20amp 12/3 wire from the main circuit box for the bathroom? My washer takes 10 amps.

Run a separate 20 amp circuit for bathrooms.

The larger wire will have a higher amp breaker and is a potential fire hazard.

A person/electrician looking at wire to breaker will assume it is that size wire on whole circuit.

It would be safe to go from smaller wire at breaker to larger wire. But not the other way around.

Chuck

Thanks for the help

I am upgrading my laundry room and my bathroom in my basement. i was going to run 8/3 wire with ground to my electric dryer and then i was going to run 10/3 wire to my washer outlet. from the washer i wanted to run 12/ 3 wire to my GFI bathroom outlet and from this outlet 12/3 wire to two other outlets, 3 can lights and a bathroom fan. can i do this or should i just run a separate 20amp 12/3 wire from the main circuit box for the bathroom? my washer takes 10 amps.Wow, there is so much wrong here I am not sure where to start.

NO, you cannot do this for several reasons. You CANNOT have the washer receptacle/circuit on a 30A breaker (unless of course it requires it), nor can you share it with the 30A dryer circuit, nor can you share it with the bathroom receptacle circuit.

Why such odd wire sizes?

Run a 10/3 to the dryer.
Run 12/2 to the washer.
Run 12/2 to the bathroom receptacles.
Run 12/2 or 14/2 to the lighting/fan circuit.

Thanks for your help