sizing natural gas grill line.

I have a 3/4 galvanized pipe coming out of my basement wall. I have a grill hooked up to 3/8 od copper
pipe for about 10 years. I just move my grill location and have new bigger 5 burner model jenn air which will be about 25 feet further. Will the 3/8 od still be big enough or should I increase the size?

Not enough information given...

Need to know the BTU of the unit. My guess, with a 5-burner unit, 3/8" that length probably won't be enough. The instruction manual of the grill will have supply pipe sizing recommendations...follow them. My guess is at least 1/2", and maybe 3/4" depending on the total distance, fittings, and BTU requirements. The manual will also state the size of the flexible hose...don't skimp there - you want the full BTU available, and restrictions may prevent that.

Why not just continue with 3/4" pipe? I doubt that 3/8" would be anywhere near enough and while 1/2" might be enough, for the amount you need, the cost difference will be minor and you'll be sure to have at least gas capacity as much as you need.

the 3/8" line wasn't big enough to run your first grill.

1. 3/8" will NOT be large enough.
2. Copper tubing will probably NOT be a proper material for the gas line.
3. The proper materials are usually NOT available to DIY or handymen.