# Thread: How much Gross Grain is left on the roll

1. ## How much Gross Grain is left on the roll

For the DIY or gear maker, it's nice to know how much gross grain, or tape, or whatever else is left on a roll, without unwinding it. I found these two formulas online and they agree with each other. I have not measured them, but they agreed with what was printed on one of my rolls of grossgrain.

L=pi*(r2^2 - r1^2)/t where

L= length of tape remaining in inches
pi=3.14
r2 = outer radius of roll in inches
r1 = radius of the cardboard core in inches (typically about .072")
t = thickness of the grossgrain in inches (typically about .0165")

Another one using diameters is:

L=pi*N*(D+d)/2 where

pi=3.14
N=(D-d)/2*t
D= outer diameter of roll in inches
d= diameter of cardboard core in inches (typically 1.45")

I use the formula in excel and enter the diameters and thickness and let Excel do the rest. I convert the the total length measurement to feet and yards. Actually having the measurement in feet is more beneficial to me making gear.

2. Originally Posted by nacra533
For the DIY or gear maker, it's nice to know how much gross grain, or tape, or whatever else is left on a roll, without unwinding it. I found these two formulas online and they agree with each other. I have not measured them, but they agreed with what was printed on one of my rolls of grossgrain.

L=pi*(r2^2 - r1^2)/t where

L= length of tape remaining in inches
pi=3.14
r2 = outer radius of roll in inches
r1 = radius of the cardboard core in inches (typically about .072")
t = thickness of the grossgrain in inches (typically about .0165")

Another one using diameters is:

L=pi*N*(D+d)/2 where

pi=3.14
N=(D-d)/2*t
D= outer diameter of roll in inches
d= diameter of cardboard core in inches (typically 1.45")

I use the formula in excel and enter the diameters and thickness and let Excel do the rest. I convert the the total length measurement to feet and yards. Actually having the measurement in feet is more beneficial to me making gear.
The first is intuitive---the area of a ring with given inner and outer radii, divided by the thickness. An approximation to what happens when the tape wraps around itself, but seemingly fine if t is small relative to (r2-r1). The second says exactly the same thing, but it seems odd to me to create D^2 - d^2 by the product (D-d)*(D+d) and then get rid of the extra 2 from D^2 = (2r)^2 with two separate divisions by 2. Huh.

3. I love when ya'll talk and type like that!!!!!
Shug.... Math Dolt

4. I would just have to keep track of how much I have used from the roll. Or unroll it and measure.

5. I have absolutely no idea what Nacra and Grizz are talking about

Syb

6. not enough

7. Uh...
was any of that in English?

It must be, I recognized the word DIY.

8. Originally Posted by GrizzlyAdams
The first is intuitive---the area of a ring with given inner and outer radii, divided by the thickness. An approximation to what happens when the tape wraps around itself, but seemingly fine if t is small relative to (r2-r1). The second says exactly the same thing, but it seems odd to me to create D^2 - d^2 by the product (D-d)*(D+d) and then get rid of the extra 2 from D^2 = (2r)^2 with two separate divisions by 2. Huh.
I thought the second one was more clutzy as well, although they give exactly the same result. When I punched it in to Ecxel, I used the fmla with the radius, then immediately miscalculated because I entered diameter. I changed my input to diamter and divided it by 2.

Here is one

Here is the other.

9. Originally Posted by nacra533
I thought the second one was more clutzy as well, although they give exactly the same result. When I punched it in to Ecxel, I used the fmla with the radius, then immediately miscalculated because I entered diameter. I changed my input to diamter and divided it by 2.

Here is one

Here is the other.
yeah. The intuitive one comes from the hoi polli on the Internet, and the clutzy one from Argonne National Laboratories. Your tax dollars at work

10. Dutch and I divided a large amount of amsteel by weighing it. (I weighed it and gave Dutch half; he hasn't complained yet.) You could do the same thing with gross grain. Might even be easier, since it's probably not wound on a core.

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