Bread stacked in red bakery cratesKnowing how many portions, or units, to take to an event is probably one of the hardest things to learn in street food. As with all catering you need to balance your sales with your wastage, but unlike most catering, stock often can’t be rolled over to the next day. At the same time if you don’t take enough stock you miss out on delicious revenue and look like an amateur to the organiser.

So this is the gamble we have to take on every event. I was recently asked how we work out our portions, and seeing as others might be wondering the same I’ll try and explain how we get our numbers.

We start with some very rough maths: The pitch fee you paid, taken as a percentage of your profits. The percentage will depend on how confident you are feeling, but will be somewhere between 10% and 30%. Don’t get too excited by that number, its probably your top end target, but it’s a nice place to start. Take that number, divide it by your average sales price and voilĂ , that’s how many units you need to bring.

Now add a little bit of realism. Ask the organiser for two numbers: the expected number of guests (g) and the number of caterers at the festival (c). More maths. Number of guests halved, divided by caterers, multiplied by your popularity index (x). Halved because at any given meal time only half of the people present will ever buy food. Popularity index because while we would all love punters to be fairly divided between each caterer, everyone who doesn’t serve hog roasts and burgers knows that this is not necessarily the case.

Your popularity index is a number between 0 and about 3, where 0 means no one eats from you at all, and 3 is a celebrity chef who could be selling the fluff out of his tumble dryer and still be doing better than everyone else. A PI of 1 represents your fair share. The number will fluctuate depending on the meal time (toasties have a higher PI at breakfast in proportion to a hog roast, for example), your audience (the younger they are, the more likely they will target the cheap burger), what your unit looks like (nearly impossible to calculate but clearly influential), how often you trade in that location (sweet, sweet repeat custom) and how much you are charging (hitting the perceived value-for-money-sweet-spot).

This calculation then gets multiplied by the number of meal times (m). If the festival involves camping you get three per day, if it’s just a daytime thing you only get one. Turn it into a fancy formula and you are presented with this:

Mmmmm, numberwang.

Mmmmm, numberwang.

Unfortunately the only way to discover your Popularity Index is to go out there and trade, then look back and work out averages. Even then, once you have added it all up, your location within the festival, the weather and how much seating is near you; Factors that you won’t be able to really judge until you arrive, all make a massive difference.

Let’s face it: The maths will only get you so far. Being able to read a festival organiser and work out if they are being hopeful or accurate, knowing how much you have sold at similar events and being close to a means of getting more stock can all make a difference. The calculations above hopefully give you an idea, but bear in mind that we’re trying to predict the future, and it’s probably best if you go ahead and factor a small margin of error just in case I’m not bang on.

A hand with the "toastie sales line" highlighted