# Thread:

1. ## Rearrange formula

Not sure if i have posted this in the correct Forum so sorry if it is incorrect But i am desperate to get this answered.

I have an existing formula that i use in work to find out the OD of a coil from the weight, width and ID of the coil but i need to change it so i can find the weight from the ID, OD and width of the coil. The Formula i use is:

OD=(SquareRoute((Coil Weight*1000/(24.66*Coil Width))+(Coil ID/2000*Coil ID/2000)))*2000

2. Originally Posted by chriscmartin
Not sure if i have posted this in the correct Forum so sorry if it is incorrect But i am desperate to get this answered.

I have an existing formula that i use in work to find out the OD of a coil from the weight, width and ID of the coil but i need to change it so i can find the weight from the ID, OD and width of the coil. The Formula i use is:

$OD=2000\left(\sqrt{\dfrac{1000W}{24.66c_w}}+\dfrac {ID}{2000} \cdot \dfrac{ID}{2000}\right)$

I've edited the quote into it's latex form to make it easier to read. However, I may have made a mistake, is that the correct equation?

edit: $W$ is coil weight and $c_w$ is coil width

3. To be honest i havent got a clue, i havent done math for ages since leaving school, it looks good to me.
Basically im trying to work this out so i can enter it in to excel so in work i can enter the OD, ID & Width and it works out the weight for me.

Thanks for your help so far

4. Start by isolating that square root and tidy up some terms

$\dfrac{OD}{2000} = \sqrt{\dfrac{1000W}{24.66c_w}} + \dfrac{(ID)^2}{4 \cdot 10^6}$

$\dfrac{OD}{2000} - \dfrac{(ID)^2}{4 \cdot 10^6}= \sqrt{\dfrac{1000W}{24.66c_w}$

To make the next step easier I will multiply $\dfrac{OD}{2000}$ by 2000/2000:

$\dfrac{2000(OD)}{4 \cdot 10^6} - \dfrac{(ID)^2}{4 \cdot 10^6}= \sqrt{\dfrac{1000W}{24.66c_w}$

This gives the same denominator so I can sum them now:

$\dfrac{2000(OD) - (ID)^2}{4 \cdot 10^6}= \sqrt{\dfrac{1000W}{24.66c_w}$

Do you know how to continue?

5. No i dont know how to continue, sorry im a complete novice

6. Square both sides

$\left(\dfrac{2000(OD) - (ID)^2}{4 \cdot 10^6}\right)^2 \cdot 24.66c_w = 1000W$

Now it's just left to isolate W. If this is for an excel formula I wouldn't bother expanding out

7. Thank you very much for your help so far i realy am greatful but could you expand it out like i first wrote it as i find it easier to understand?

I know im being a lil cheeky but thanks for your help.

8. Thread closed because the OP needs someone in person to do this for them, not anonymous internet helpers.
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