# Supply Line Size

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#### wwhitney

or would there ever be a reason to go from 3/4 copper to 1 inch copper?
Not following the previous discussion, but there's a simple answer to the above: Every foot of 3/4" copper (type L, 0.785" ID) is equivalent to a certain length of 1" copper (type L, 1.025" ID). That length is (1.025/0.785)^4.87, where 4.87 is an empirically determined exponent. In other words, one foot of 3/4" type L copper is equivalent to 44" of 1" type L copper.

That means if you had a situation where you wanted to extend a 3/4" copper line by, say, 44', but the charts or computations say you'll be out of compliance if you extend it more than, say, 20', you can instead extend it with 1" copper and treat that extension as if it were only 12' of 3/4".

So yes, there can be a reason to go larger downstream when making modifications. If starting from scratch, putting the larger pipe upstream where it is supplying more fixtures gives you a greater benefit.

Cheers, Wayne

#### Claraarcher

##### Member
Not following the previous discussion, but there's a simple answer to the above: Every foot of 3/4" copper (type L, 0.785" ID) is equivalent to a certain length of 1" copper (type L, 1.025" ID). That length is (1.025/0.785)^4.87, where 4.87 is an empirically determined exponent. In other words, one foot of 3/4" type L copper is equivalent to 44" of 1" type L copper.

That means if you had a situation where you wanted to extend a 3/4" copper line by, say, 44', but the charts or computations say you'll be out of compliance if you extend it more than, say, 20', you can instead extend it with 1" copper and treat that extension as if it were only 12' of 3/4".

So yes, there can be a reason to go larger downstream when making modifications. If starting from scratch, putting the larger pipe upstream where it is supplying more fixtures gives you a greater benefit.

Cheers, Wayne

good info thanks!

#### Jeff H Young

i grew up in a 3 story house with 3 full baths, washer, hot water tank 2 hose bibs, a slop sing and hot water heating and it was all 3/4 and 1/2 lol. now we have more efficient stuff and i need bigger pipe - lol
yea I'm amazed at some of the undersized plumbing I don't like to undersize work and hope it works or that by undersizing cause premature wear and failure or water hammer.
sometimes conditions allow or require a bit of compromise but I wouldn't be running less than 3/4 for 2 bathrooms

#### Claraarcher

##### Member
yea I'm amazed at some of the undersized plumbing I don't like to undersize work and hope it works or that by undersizing cause premature wear and failure or water hammer.
sometimes conditions allow or require a bit of compromise but I wouldn't be running less than 3/4 for 2 bathrooms
yea think it better to open up some sheetrock and run 3/4 to everything. I'll do PEX as that much copper is a lot of \$ and i am sure i under estimated or left something out.

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Hey, wait a minute.

This is awkward, but...

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