The Mathematics of Packing

**This post’s content and format was inspired by The Simple Dollar.**

You can bring 100lbs+ to school but can only return home with 50lb and now you have to decide what stays and what goes. Ready to pull out your hair?

When coming to the islands (either Grenada or St. Vincent), a typical flight takes you to San Juan on American Airlines followed by a prop plane taking you the rest of the way (American Eagle, Caribbean Star/Sun, Liat, etc.). To benefit from the business of the larger companies, these smaller island carriers agree to handle the promised luggage allowance. So coming to the islands, I was allowed 2 x 50lb checked luggage, 1 x 40lb carry on and a 1 x personal bag not to exceed 15lb. For those keeping track at home, that’s 155lbs.

These smaller airlines have smaller airplanes and so cannot possibly take all of this promised luggage, so instead they take what they can with each flight and come back for the rest later. This means that most students coming to the islands wait a few days to receive everything.

Going back is a different story. The larger airline may have changed its guidlines and will now allow two checked bags not to exceed 70lbs in total (that’s a loss of 30lbs) or the smaller airline may decide (at their discretion) not to honor your previous luggage allowance when leaving the islands and restrict you to a single 50lb bag.

So what are you to do? Many students donate piles on piles of clothes to charity, others pay FedEx or Amerijet to ship their items home, but very rarely is this cost effective. Why pay $200 to ship 40lbs of used books? So nerd that I am, I suggest the following:

Let’s say you have the worst case scenario of one 50lb bag and one carry on. First, weigh the bag and subtract that from the total. If you have a soft bag with rollers and a metal back brace housing a retractable handle, this weighs around 7lbs.

Now that we’re only working with 43lbs, it’s time to separate the wheat from the chaff.

  1. Identify items that are truly invaluable i.e. they cannot be replaced and under any circumstances (non-digital photos, hand-written lecture notes, annoying yearbook you made everyone sign). Weigh these and place them in your bag. Subtract from total.
    1. This category does not include your computer, digital camera, text books, etc. as these can be replaced.
  2. Assign each item a packing coefficient (Cp). To do this, decide the monetary value of an item and divide that by its weight. Your coefficient for each item will be in units of $/lb. Here are a few examples:
    1. Braun Activator Shaver, used one year. Originally $150 now $80. Weight 6 ounces (half a pound).
      1. Cp = $80/0.5lb = $160/lb. A high coefficient!
    2. Motioncomputing Tablet Computer, used two years. Originally $3,000 now $1800. Weight 3lb.
      1. Cp = $1,800/3lb = $600/lb. Extremely high coefficient.
    3. Hanes white t-shirt, used one year. Originally $1.5 now $0.1. Weight 2 ounces.
      1. Cp = $0.1/0.125lb = $0.8/lb. Should probably just throw away.
  3. Rank your items in a descending fashion.
    1. calculatorInvaluables Cp =
    2. Motion Computer Cp = 600
    3. Braun Shaver Cp = 160
    4. Little black dress Cp = 30
    5. Blue Jeans Cp = 15
    6. Beloved Merck Manual Cp = 13!
    7. Beloved Golian Principles of Pharmacology textbook Cp = 10!
    8. Cargo shorts = 3
    9. T-shirt Cp = 0.8
  4. Increase the worth of your suitcase by filling it, starting with the highest Cp items and working your way down until you have reached your weight limit.
  5. Armed with the knowledge that it costs you money to bring anything else, donate the rest to charity!

While I expected most of my shirts to be worthless, I was shocked to find that my beloved textbooks were worth less for their weight than my denim jeans (the little black dress is for illustration, I do not wear dresses in my spare time). Had I not gone through this exercise (originally for fun, I’ll admit), I certainly would have tried to save the books and then lost money back home buying a new pair of pants.

Ahh, the fruits of nerd labor.

DISCLAIMER: Stictly using Cp is effective if we assume that the space that each item occupies is negligable, i.e. to be truly complete we would have to factor in the volume that each item occupied and for that calculation, price/density (price/mass/volume) would have been more appropriate.

For example, nice bedding with a Cp of 40 might end up taking half the space in your luggage, thereby preventing you from using that same space to add more items at lower Cp, the sum of which would exceed the bedding’s worth. Fortunately, this is rarely an issue and we can concern ourselves with price and pounds alone.

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5 Responses to The Mathematics of Packing

  1. nosugrefneb says:

    You must be really bored. This was almost as nerdy as some of my posts!

    Why not just transfer some of the heavier but more valuable stuff to carry-on? Or is that regulated too?

  2. The carry-on is always weighed. The only things that are not regularly weighed are the personal items (purse, backpack, briefcase) because it is assumed that these are of negligible weight. This represents an opportunity to bring things outside of the radar, but should it “look” heavy i.e. you’re groaning under the weight, they will ask you to weigh it and then either check it or discard until it is under 15 lbs.

    And yes, I am bored.

  3. nosugrefneb says:

    Ah, bummer. It’s pretty obvious to me, then, that your next best option is to start surgically implanting items in your abdomen, e.g. tablet, physio texts, canned foods, drugs, etc. You know, the basics. Or, swallow them and poop ’em out later. They’re not weighing you, are they? :)

  4. Too much analysis. Cram it in and see how heavy it is. Remove cheap heavy items until you don’t feel herniated lifting it. Replace the missing items when you get there – if you’re heading for home you can leave them there and you don’t have so much of a pain on your next trip.
    I used to agonise on forgetting something when I travelled and then decided it wasn’t worth the aggravation

  5. Adrian says:

    Obviously medical school is not time consuming enough for you, Topher!

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