What is a good length or number of routines for a quick impromptu show?

Depends on the mood of the people you are showing it too. Are they simply curious but not really interested? Then make it short. If you're getting great reactions and they keep asking you to show more, then show more.

Hi Andy,

To an extent I agree with shalhorowitz0. But, I think you can structure a routine that builds up in such a way that you know that you can stop at any point and it will be amazing. Here you have some thoughts I gathered from "Strong Magic" by Darwin Ortiz, and other places.

You can plan on 3-5 tricks for a good routine. It feels right. If you do three you can do an Opener, a filler, and a closer. Or you can do an Opener, 3 fillers, and a closer. You can also play it by ear if you follow the next tips.

You have to decide what a good opener would be, and what a good closer would be, anything else can be more or less planned depending on your personality, and amount of material you can do. I think there are two types of Openers

Openers
1) Introductory: The type you would do if people are not expecting you to do magic, or if they don't know you are a magician. It has to be something where the magic happens super fast, and places you in an unthreatening, or friendly position towards the spectators. So, if you said you found this wallet and you want to give it back places you as the center of attention, as a friendly stranger, then the fire goes in flames as you look for the driver's licence, and they realize you're a magician with a smile. You can also ask someone if they dropped a coin and make it vanish as you give it to them, and do a quick coin routine. This will gather a smaller crowd, but the person who sees the trick will tell their friends immediately. I think David Stone goes in more detail about this in the Real Secrets of Magic. After the effect you can ask, or feel if they are excited and want more, and you can go on to the next type of opener. (I wouldn't count this effect as one of the 3 if you are following the rule of 3 or 5, because some people will miss it).
2) Regular Opener: a Quick effect when you don't need to introduce yourself. You would do this if the people you are with already know you are a magician, or if you already did an introductory trick, and they want to see more. Again, this trick also needs to be really quick. Most tricks are either based on Surprise or on Suspense. You don't want a suspense trick here (this is also from Darwin Ortiz). You want something that happens quick and that they are not expecting. I find that any production from flash paper is a great grabber. I normally make my deck appear if I'm doing card work. I make a dollar bill or a coin appear if I'm doing something with money. You can also do a quick coin bend, and this will get them all wanting to work with you as they bring out their coins. You can do some Voodoo ashes if people are smoking, something like that.

Fillers:

These are all other tricks. I would try to do tricks that are gradually more impressive in an ideal world, or you can make them seem more impressive by what you say, but you can play it by ear too.

Closers:
You want your closer to be a trick with multiple climaxes, or one that has a lot of suspense built into the routine(if you need me to clarify let me know, but this is getting pretty long). In both cases the feeling generated inside the spectator is that of building up of emotion and release at the final climax that will hopefully make them burst into excitement, or clapping, and preferably jumping up and down as they scratch their faces and loose control of all civility and composure.

Knowing all these points you can do just one trick (introductory, or regular opener, depending on the crowd), three, five, six, or fifteen, which I wouldn't recommend. One final thought. If you are not sure if they will ask for more after you're done have two possible closers save the better one for the second ending, but try not to go on after you have no closer in mind, otherwise everyone will end up with mixed feelings, and you want the jumping up and down, loss of composure, etc.

I hope this helps!!!

PS. If you want to figure out a profesional routine, I follow the 3-5 tricks rule for close-up, and 45mins. of material for a larger crowd.

I try to limit it to one; maybe two, strong effects. Anymore than that in an informal setting would probably be too much.

Good advice Pepe
Todd