Ken- Spokes are usually measured from the inside edge of the elbow to the end of the threads at the other end. Other ways put: if you were to hook a spoke on the end of a metal rule and let it dangle down along the scale, where the threads ended would be the spoke's length. There are fancy calculations to compute spoke length if you don't have one to measure directly as well as on line programs to do this for you. When I do broken spoke replacement repairs I often remove an adjacent spoke (on the same side of the wheel) and measure it. Some times I'll add or subtract a bit to correct for the original spoke's not being the "best" length (when tightened the threaded end should rest at the nipple's slot base, or about 1mm below the nipple's head).
The simplest method to replace all the spokes is to loosen all until the rim flops a bit. Remove and replace one spoke at a time keeping the pattern and over/under interlace the same. When all the spokes are replaced then consistent retensioning and actual truing/dishing can follow. Tension/dishing/truing advice will take more time then we have space for here but again there's a lot of on line information. Google "wheelbuilding".
Don't forget to have a beer at hand.
> Message: 1
> Date: Wed, 26 Aug 2009 09:39:25 +0100
> From: <kfhume@hotmail.com>
> Subject: [CR] Clicking Spokes III
> To: <classicrendezvous@bikelist.org>
> Message-ID: <BLU107-DAV593D5821C34BF731B274ED7F70@phx.gbl>
> Content-Type: text/plain; format=flowed; charset="iso-8859-1";
> reply-type=original
>
> Hi,
>
> I have decided to have a go at replacing all the spokes in my 700C front
> wheel with new stainless spokes.
>
> When ordering spokes on the web there appears to be a huge range of spoke
> lengths from which a choice has to be made.
>
> My question is how does one measure the length of an existing spoke so
> that
> the new spokes will fit properly.
>
> Is there a preferred simple proceedure to be followed to change the spokes
> and realign the wheel ?
>
> Regards
>
> Ken Hume
> London, England.
Andrew R Stewart
Raleigh, NC