Calculating Purchasing Quantities
With menus that change daily, more time and planning is required to properly order product. While many of the products in your inventory will remain constant, there will be many new items that you will need to purchase for a specific menu. As mentioned, nothing replaces experience. Most Chefs have their own routines and methods for ordering. What works for me, may not work best for you. What we are going to discuss are the basic procedures for calculating quantities needed and other considerations when ordering. Purchasing all
comes down to simple math. Quantity Needed – Quantity On Hand = Quantity Purchased. But, how do we determine quantity needed? For some items it’s much easier to determine, while other items may take a few more steps.
Let’s say we are making Pumpkin Pies for a Thanksgiving Dinner. The recipe says each #10 can of pumpkin puree (106 oz) makes six  10” pies and each pie will be cut into six servings. A case of #10 cans of pumpkin puree has six cans per case and there are 20 10” frozen pie shells per case. We are expecting to serve 325 people for dinner that evening. In order to figure out how much we need to order, we first need to figure out how many portions or pies we need to make.
If we are expecting 325 guests, what percentage of the guest do you think will order the pumpkin pie for dessert? Pumpkin pie is a Thanksgiving tradition and you are known for your pies so let’s estimate that 70% of the guest will have a slice. This 70% represents our Acceptance Factor, or what percentage of our guests will want that product.
If you are serving other desserts, the total acceptance factor for all desserts should not exceed 100%. If the total is more than 100%, this would mean that you are selling more desserts than the total number of expected guest,Pumpkin Pie – 70% = 228 Portions

Cheese Cake – 12% = 39 Portions

Pecan Pie – 12% = 39 Portions

Black Forrest Cake – 5%  16 Portions

No Dessert – 1%

100% and 322 Total Portions
To figure out how many portions you need, you will multiply 325 guests by 70% (325 x .70) = 228 portions needed. If 228 portions are needed and you get 6 slices per pie, you will now divide 228 (number of portions needed) by 6 (number of slices per pie) 228 ÷ 6 = 38 pies needed.
We said we get 6  10” pies per can of pumpkin so we now divide the number of pies needed by the yield per can 38 ÷ 6 = 6 cans. If there are 6 cans per case you will need to order one case of pumpkin and 2 cases of pie shells 38 ÷ 20 = 2 cases.
To Summarize:
325 Guest and 70% will order Pie 325 x 70% = 228 portions

228 portions needed divided by number of slices per pie 228 6 = 38 pies needed

38 pies divided by the yield of each can of pumpkin = 38 ÷ 6 = 6.33 cans of pumpkin or 1 case. (Imagine we have one can in the store room)

38 pies needed and there are 20 10” pie shells per case so you will divide 38 ÷ 20 = 1.9 or 2 cases of pie shells

Quantities needed 1 Case Pumpkin Puree 2 Cases 10” Pie Shells
Now you need to order Turkey’s for the dinner. This requires a few additional considerations for ordering. The last thing you want to do is run out of Turkey on Thanksgiving. For the ease of preparation, you spec out a boneless netted raw turkey breast that has an 1114 lb. average with 2 pieces per case. For the purpose of this exercise, we will say each turkey weighs 12 lbs. (AP Weight). So let’s first determine how many portions of turkey we will need. As with our desserts, we will be serving other entrees. Our first step again is to estimate the acceptance factor for each entrée and calculate how many portions of each will be needed.

Turkey – 80% = 260 Portions

Prime Rib – 15% = 49 Portions

Grilled Salmon – 5% = 16 Portions

100% and 325 total portions
We now know that we need 260 portions of turkey and our determined portion size will be 5 oz. (EP) portion per entrée. So we can now easily determine that we will need a total of 81.25 total pounds of turkey by using the formula:
Portions Needed x Portion Size ÷ 16 oz. = 81.25 Total Pounds
260 x 5 oz. = 1,300 total oz. ÷ 16 oz. in a pound = 81.25 lbs.
With a total weight of 81.25 lbs. which we will round up to 82 lbs. We can calculate how many cases we need to order by using the formula:
Total Weight Needed ÷ Total Case Weight = Number of Cases to Order
82 lbs. ÷ 24 lbs. case (2 – 12 lbs. Pieces) = 3.42 cases which we will round up to 4 cases.
With each turkey breast weighing 12 lbs. and a determined 5 oz. portion, we calculate that we will get 38.4 portions per breast (12 lbs. x 16 oz. = 192 total oz. ÷ 5 oz. portion size = 38.4 portions). With a total of 8 turkey breasts getting 38.4 portions each, we will have 307 portions of turkey, giving us 47 portions more than what we calculated we will need.
While this seems to be accurate, there are a few things to consider. First, when we cook the turkeys, there will be loss of weight due to the loss of liquid from the breast. We will estimate that there will be an 8% weight loss of each breast when cooking. This now means our 12 lbs. breast will weigh 11 lbs. 4 oz. after cooking.
12 lbs. x 16 oz. = 192 total oz. x 8% weight loss = 176.64 total weight ÷ 16 oz. = 11.04 lbs. Giving us a new portion yield of 35.32 portions per breast.
We lost 3 portions per breast and that is if we utilize 100% of the meat. We need to take into consideration that there will be loss due to trim and waste.
We now estimate that we will lose another 5% to trim and waste, bringing our new weight of the breast to 10.48 lbs. (EP Weight). losing 1.5 lbs. of each breast to cooking and trim.
11.04 lbs x 16 oz. = 176.64 total oz. x 5% Trim and Waste = 167.80 oz. total weight ÷ 16 oz. = 10.49 lbs. total EP weight
giving us a new portion yield of 33.6 portions per breast, 5 fewer portions than originally thought.
Going back to our original calculations of needing 812 lbs. turkey breasts to cover the 260 portions we will need for service, we now need to calculate based on our new yields whether or not this will still be enough turkey. We calculated that we would need a total of 82 lbs. (EP) for the 260  5 oz. portions. We determined that there will be 1.56 lbs. loss per breast, giving a 12 lbs. breast (AP Weight) a yield of 10.44 lbs. (EP Weight), so a 24 lbs. case will give us 20.88 lbs. (EP). Going back to our formula:
Total Weight Needed ÷ Total Case Weight = Number of Cases to Order
82 lbs. ÷ 20.88 lbs. case (2 – 12 lbs. Pieces) = 3.93 cases which increased ½ a case from our original calculation of needing 3.42 cases dropping our yield from 307 portions to 264 portions from the 4 cases of breast.
Now the decision becomes; will this be cutting it too close only ordering the 4 cases? What happens if more people want turkey? What happens if the trim and waste is actually closer to 8% or if the cooking weight loss is higher? These are all questions that need to be taken into consideration when planning and ordering. While you do not want to be left with way too much product, you certainly do not want to run out as well. With a product like turkey, I would lean towards buying another case, because it is a product that can be utilized in many applications and the cost of the product is relatively inexpensive.
The process of calculating how much to order seems more complicated than it actually is. Though it does require a little work, the benefits far exceed the negatives of not taking the time to properly calculate how much to order. This process will not be needed for every product, but should be used to some degree to get an accurate amount needed.
This is only part of the equation in calculating amounts to be ordered. There are other factors such as the style of service you will be using.
Planning and ordering for a buffet event is different than ordering when you control the portions. This is the mere basics of determining how much to order to help you understand how ordering needs to approached. If you’re lucky, you have a menu management system that will help you determine your purchasing needs. As helpful as they are, please keep in mind that the system does not know your business or what you have in house. A menu management system is another tool to assist you in your business and will not replace knowledge and experience.