You might want to post this over on the Vegetable Gardening forum for more answers (the focus on this forum is canning and preserving). I linked that forum for you below.

The average listed yield for a 10' row of spinach (depending on the variety used) is 5 lbs. This assumes whole plant harvesting.

Here is a yield chart put out by U of Iowa.

Johnny's Selected Seeds also has a great yield chart in their catalog and on their website.

Hope this helps.

Dave

Here is a link that might be useful: Vegetable Gardening forum

Spinach can be a very difficult crop--it bolts rapidly from a combination of temperature and increasing day length. A better choice might be Swiss Chard. It will produce all summer, is much easier to grow, and yield will be greater than with an equal planting of spinach. Once cooked, most people can't tell it from spinach.

I certainly agree that Swiss Chard is a wonderful choice but don't be afraid of spinach either. I live in TX and I get it in the ground early and it produces a wonderful crop. I don't harvest the plant just the leaves and have a come again bed and it will eventually bolt because of the heat but before it does, I get tons of spinach and it doesn't bolt until it's really hot....I have a 16 foot bed and it produces enough to eat regularly and to give me plenty to freeze. I plant it thick too......