On Thu, 19 Jul 2018 18:28:59 -0700 (PDT), trader_4
wrote:

On Thursday, July 19, 2018 at 8:47:21 PM UTC-4, Ed Pawlowski wrote:
On 7/19/2018 6:44 PM, Terry wrote:
replying to trader4, Terry wrote:
Im building a pergola , how far can I span with a 2x8 treated beam.
Needing
to be 14.

With no load you can go pretty far. It only has to support itself on a
pergola. You will be good for 14'

Yes and if he googles for floor loading calculator, joist calculator,
beam calculator there are tools online that will give you the various
options depending on the load, span, spacing, type of lumber

They spanned 12' with 2x8 hem/fir around 14" O/C in my house in Md and
it never fell down. The design load was around 40 per sq/ft as I
recall.
Like Ed says, in a pergola where there is not much else up there it
should be fine unless they strap the top with 1x4s to block the sun
and you end up with a snow load. The one that was here in Florida when
I moved in was spanning 13' with 2x6 SYP.