I'm part of a group of seven people looking to paint along with an episode of Bob Ross, and I'm trying to buy supplies for the group, but we've never painted before.
How far would a single 5oz tube of a given color (e.g. Alizarin Crimson) go? Would one of those be enough for seven people to do two paintings each?
We've selected one of the paintings we will be doing:
This is Grandeur of Summer by Bob Ross.
The amount of paint you will use depends both on the size of the painting and your personal style and technique. The amount of paint you use may be more or less than another person in your group.
Others have asked this specific question, e.g. "Amount of paint used in a typical Bob Ross painting" https://www.reddit.com/r/HappyTrees/comments/6d29w8/amount_of_paint_used_in_a_typical_bob_ross/
As you can see by the range of answers, again, there is no mathematical way to calculate how many tubes/grams of paint you will need.
Once you have painted for a while, you will know approximately how much paint you typically use. In the mean time, I suggest visiting a local art supply store if there is one in your area, and ask for their advice. You may be able to buy more paint than you think you will use and return unopened tubes. But we sure to ask about returns before you purchase.
This sounds like a great group activity and a lot of fun.
I'm not an oil painter, but do remember that you'll also need mediums to mix into your oil paints as you work in order to control the thickness and transparency of the paint and to clean your brushes.
Five ounces is a fairly good-sized tube and I'd expect you'll have plenty as long as your paintings aren't terribly large and you keep the painting surface smooth rather than highly textured (impasto). Nine by twelve inches is a typical student size--large enough for ease of work but small enough to be manageable for a beginner. The colors you will usually need the most of are white, yellow, and whichever brown Bob has you using. The other colors (reds, blues) tend to be very saturated. In most cases you'll be mixing fairly small amounts of them with your medium or with white or yellow.
