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'Treegonometry' uses math for perfect Xmas tree

U.K. students calculate a math formula for just the right proportion of tree decorations. Their efforts won't win a Nobel Prize, but they do add up to a bit of festive fun.

But what size should the kitten be?
Bernie McGinn

Let's say you just bought a 6-foot Christmas tree and want to decorate it just so. According to a quick treegonometric calculation, you should use approximately 30 feet of tinsel. (I got that number, incidentally, by multiplying pi by 13, dividing that number by 8, and then multiplying that figure by the tree's height in centimeters.)

Didn't study treegonometry in high school? That's because it just got invented by members of the University of Sheffield's SUMS math society. Two students at the U.K. school set out to calculate the amount of baubles, tinsel, and lights needed to give a tree just the right amount of decorative zing.

Their math might not add up to anything worthy of complex analysis, but it's a festive and amusing idea. "The formulas took us about two hours to complete," 20-year-old student Nicole Wrightham said in a release. "We hope the formulas will play a part in making Christmas that little bit easier for everyone."

The students concocted their equations in response to a challenge issued by British department store Debenhams, which no doubt sells oodles and oodles of baubles and Boodles.

"Customers are often making the error of buying too large or small an angel; however this simple formula means you'll have the tree-to-star ratio correct," said Debenhams Christmas decorations buyer Sarah Theobold.

Oh, and for the record, if you're a stickler for getting that ratio "right," you can try dividing the height of your tree (in centimeters) by 10.

Not one for math calculations? Wrightham and cohort Alex Craig have created an online calculator that does the math for you. Metric conversions, however, are your job.

This year's Trafalgar Square tree is about 69 feet tall, meaning it would need 433 baubles, more than 328 feet of tinsel, 213 feet of lights, and a 6.5-foot-tall star, the students say. University of Sheffield