The roasted chicken recipe I'm following of course calls for kosher salt, but I don't have any, and getting some is out of the question.
I have sea salt and table salt on hand.
Can I substitute one of those instead, and if so, what is the proper ratio of the kosher salt the recipe calls for to either sea salt or table salt?
I don't know how well a substitution will work in this case, because I don't know how the salt is being used in the recipe.
If you're mixing the salt into something where it will dissolve, then go ahead and substitute, using the chart that @ManiacZX linked to. If you're mixing it into cold things, and it doesn't sit for very long, I'd go with a finer salt if you have it.
If it's a recipe that calls for a salt rub, where you rub the bird down with salt, let it sit, then pat dry and roast, you're not going to have as good of results with a replacement. The issue is the size and shape of the crystals; kosher salt specifically sticks well to moist surfaces to draw out the liquid, and as a result, some of the salt is taken into the meat. You're not going to get the same behavior with other salts (or at least, not in the same amount of time).
Yes you can substitute.
If you are measuring by volume, e.g. 1/2 tsp then you need to adjust as appropriate for the size of the salt granules.
1 tsp of table salt is much more salt than 1 tsp of kosher salt. The tiny grains pack together much closer, giving you more salt.
That said, sea salt is typically closer to the size of kosher salt granules; so use that.
There is no hard and fast ratio. If the grains are smaller use a little less; if bigger use a little more.
Finally, if the recipe calls for salt by weight, then they are all equivalently interchangeable.
You can substitute between kosher, table and sea salt.
The issue in the amount for substitution is the difference of size in the grains of salt cause volume measurements to not equal the same amount of salt.
Here is a conversion chart from Morton, should be a good guideline. http://www.mortonsalt.com/for-your-home/culinary-salts/salt-conversion-chart
People are missing a big factor in what defines Kosher salt -- the absence of any additives, especially iodine (as in iodized salt). If it is being used for the lactose-fermentation process, such as when making kimchi or sauerkraut, iodine will greatly affect the process in a very bad way, so something like Kosher salt is needed. The grain size is less important, but a larger grain is preferred.
