Editors note: New 2013 Chart available here.
A reasonable estimate of the Atlantic Giant Pumpkin weight can be found by taking careful measurements and then using a formula to calculate the weight. These calculations yield results that are within plus or minus 5%. The formulas are based on the original work of Bob Marcellus. Bob collected and tabulated the Over The Top measurements for many pumpkins over a number of years. His tables for estimating weight from circumference or OTT measurements appeared in the book "How-To-Grow World Class Giant Pumpkins, II", by Don Langevin and published by Annedawn Publishing, Norton, MA.
The key problem for the new grower is first, how to correctly make the measurements and second, how to do the math. Once I show you how to make the measurements all we need to do is get past the math stumbling block. Fortunately, most people have access to computers these days so it becomes a matter of following a 'cookbook recipe' and you never need to understand raising a number to a power or exponents or any of that long forgotten math.
To begin this project we first need a model pumpkin. Lucky for me, today is the day I have decided to cull a sorry misshapen example of how not to grow a giant pumpkin. This pumpkin insisted on growing 'stem down' and the chance it would successfully reach maturity was slim so off with his head. Now lets see if even this malformed example can make a contribution to pumpkin society as a model for our measuring tutorial. Remember that the equations are claimed to predict the weight within 5% even for our less than stellar example. See Figure 1 below.
The first measurement we need is the circumference. That is the distance around the fattest part of the pumpkin parallel to the ground. For this we need a soft cloth tape measure. Now, I know what fabric stores are for. Nobody makes clothes these days, they're too busy growing giant pumpkins so this is the store where we go to buy pumpkin-measuring tools. As you can not see, the circumference is 63 1/4 inches. Be very careful when making measurements, the pumpkins are easily scratched. Who wants a defaced pumpkin or worse yet a fatal infection. See Figure 2 below.
The next 2 measurements are literally over the top (OTT). Do NOT follow the contour of the pumpkin to the ground. One measurement is from the ground straight up to the fattest part of the pumpkin, over the top and straight down to the ground. Do this for the stem end over to the blossom end and then from one side over to the opposite side and down to the ground. (in this case to my deck) See Figure 3 below.
Our champion measures 45" blossom to stem (BS) and 45 5/8" side to side (SS).
Now for the easy part. There are 2 methods (equations) for calculating the weight. One is based only on the circumference and the other uses the sum of our OTT measurements. The circumference method is better for day to day comparisons to see how fast the pumpkin is growing while the OTT method yields a better estimate of the real weight. In our hero's case, circumference was equal to 63 1/4" and the OTT equals (63 1/4 + 45 + 45 5/8) 153 7/8". Only the mathematicians want to know that the weight of the pumpkin is equal to 0.001517*POWER(circumference,2.61374) or
The rest of you want to know how much does it weigh. Fire up your spreadsheet and fill it in as below. Column A will have your circumference (thatís why it is labeled C in cell A3. Column B will have blossom to stem (BS) and you guessed it column C will have your side to side measurements. For column D, click in the cell D4 then press the large + key and type SUM(A4:C4) and press enter. For column E, click in the cell E4 then press the large + key and type 0.0000795*POWER(D4,2.76) and press enter. For the last column F, click in the cell F4 then press the large + key and type 0.001517*POWER(A4,2.61374) and press enter. Now, whenever you enter your C, BS, and SS measurements the OTT column will automatically show the sum and the E and F columns will show the calculated weights. (someday this will all be a built-in function on your Pumpkin-Pilot XXIV) You can see by the OTT method our hero weighs 86.6. See Figure 5 below.
How does this compare with our pumpkins real weight? Well draft one teenage son and a scale. "Boy, pickup that wet pumpkin and get on the scale. 236 pounds. Carefully put the pumpkin down and then get back on the scale. Hmm, one boy minus the pumpkin, 154 pounds." This math we can handle. The pumpkin weighs 82 pounds. Ok so its calculated weight is 5.6% more than its real weight. I lied, missed by 0.6%. The equations vary from year to year as more pumpkins are used to derive the equations but they don't change much and we just want to know which pumpkin is growing faster and a reasonable bragging estimate until weigh-off.