The only thing worse than being up the creek without a paddle is going down the creek with an incorrectly fitted one.  If your paddle doesn't suit your size and paddling style, you're not going to enjoy doing it.  

Some paddle companies have created a science out of fitting kayak paddles, and it's daunting to get lost in all variables.  We've tried to simplify things here yet cover the important points.  Here's what you need to consider:

Boat width

The wider your boat, the longer the paddle you'll need.  If you are paddling an ark, you'll pretty much need a lodgepole pine to clear that beam.  Narrow boats let you get the blade in nearer to your body so you don't need as long a shaft.  Boat width is probably the most important factor in choosing paddle length if you're a recreational paddler.   

Blade shape

This factor is more important if you're into touring or sea kayaking.  Here you need to consider what style of paddling you like: low angle or high angle.  Many recreational and touring paddlers prefer low angle which is easier on the body because you are in a more relaxed position.  If you have any arm joint issues, this is the style for you.  Low angle paddles tend to have longer, narrower blades.

Athletic paddlers who like to get a little more power into their stroke may prefer high angle paddling.  The paddle shaft is more vertical during this type of stroke and the blades tend to be shorter and wider than low angle blades.   You can think of it as paddling in a higher gear.

Here are some tables done by the good folks at Werner Paddles showing recommended paddle length based on boat width and paddler's height:

Shaft size 

Pick a shaft that fits your hand.  That may mean a regular straight shaft, an ergonomic bent shaft that releases strain on the wrist (but adds a little bit of weight), or a smaller diameter shaft if you have petite hands.

Quick test

Pick up a kayak paddle and hold it horizontally in front of you.  Check that your elbows are bent at ninety degree angles, and take a look at where your hands end up on the shaft.  Each hand should be about two thirds of the way between the centre of the paddle shaft and the point where the shaft meets the blade.

Conclusion

Good quality paddles can be expensive.  The more you spend, the better your paddling experience will be.  The paddles get lighter, stiffer, and have far superior ferrules than cheaper paddles. 

Before you commit to a paddle, consider how much you are willing to spend.  Add a little more onto that figure and then go for it.   We've never had anyone come in regretting how much money they spent on that lightweight carbon fibre paddle... but we have had people wishing they'd gone for the better paddle in the first place.

Just remember, you will be swinging that paddle around for hours... make sure it doesn't feel like a kettlebell workout :)

And just to whet your appetite, here's a short video by Werner Paddles on proper forward stroke.

The Basics for Easier Paddling-Forward Stroke from Werner Paddles on Vimeo.