Hi,

I would like to by paddle for wave surfing on my sup.

I already have paddle for rowing which is length is ok but too long for surfing.

What the paddle length should be comparing to my height if it is only for wave surfing? Is it ok if its length is equal to my height or should it be taller and how much?

TIA

completely personal preference, I have mine about 1 inch taller than my height for all round conditions...

if you ride with a longboard style, I don't think it's very important to worry about - if it's a bit longer, but if u ride a short board sup at a decent level, I do think it matters.

From head high to about 8 inches longer.
I started with about 8 inches longer than my height. Then my paddle blade broke away from the end of the shaft due to a bad paddle design. So once re cut & repaired it was about 1 inch more than my height. Which sort of made me use more of my body than just arms & shoulders & I think more power.
But I found my short paddle damages the rails of a board more due to the blade hitting the rails more so than the shaft of a longer paddle which hardly makes any damage.
So my preference for my paddle length will be about 6 inches longer than my height.
And I believe a longer paddle is better for foilboarding too because of the extra height off the water surface.
I don't feel much difference anyway.

Just use a paddle length equal to your height. That's the reference length for SUP surfing.

Then you can try to reduce the length more. A shorter paddle is useful for radical surfing in small waves, where the paddle bulk can prevent tightening your turns and surfing close to the pocket. But it is more tiring, as it forces you to flex your knees more... which also helps keeping balance in chop.

I used to have 3 paddles of my length (+0"), +2" and -2". But I broke my +2" and never replaced it.

Head high to hairline for wave riding. Shorter boards prefer shorter paddles. Bend those knees get the hosel in the water..

Eye height for me, seems to encourage a lower stable stance whilst paddling in

See. There you go eran. Everyone is different. From overhead down to eye level.
But one thing is certain. If you go too short first off you basically cannot go longer. But if you start longer you can remove the handle, cut the paddle a little shorter until you have the desired length paddle you need.
I would advise anyone starting out with paddleboarding to get an adjustable paddle first so adjustments can be made. Then buy a fixed length paddle & cut to that desired length.
Then you will always have a spare paddle in case you break your fixed length one.

I cut mine down to eye level after a couple of years at my height.
I enjoy it more now, I get more aggressive paddling for wave, lower weight forward. Plus feels nice in turns.
All personal choice, work your way to a shorter paddle a bit at a time.