# Calculating Rod Length in CADmep & ESTmep

In this article, I want to show you how CADmep or ESTmep calculate the rod length. We can use two methods, the first one is using a constant length that you could define in your database. The second one is using the soffit from the section where the duct is. In both cases, CADmep and ESTmep use the same formula.
The formula is:

Duct height x2 + rod Extn x 2 +  rod Extn Above x2

### First Method

For instance I have a duct 400 mm x 400 mm ; Elevation 1200 mm ; Soffit 3000 mm

I can set the “Rod Extn” in my data base to 500 mm which is the default value

The formula is :

Duct height x 2 + rod Extn x 2 +  rod Extn Above x 2

Which is :

400 mm x 2 + 500 mm x 2 + 50 mm x 2 = 1.9 m

You will find the result in the cost breakdown. (see image below)

### Second Method

I am still using the same duct 400mm x 400mm ; Elevation 1200 mm ; Soffit 3000 mm
Now, If we set the Rod Extn to 0, in your database.(see image below)

The “Rod Extn below” will be (Soffit – (Duct height + Elevation below duct)).

Which is:

3000 mm – 400 mm + 1200 mm = 1600 mm

You will find this information is automatically calculate for you in the Take off interface as the “Rod Extn Above”. (see image below)

So the formula is still the same :

Duct height x 2 + rod Extn x 2 +  rod Extn Above x 2

Which is :

400 x 2 + 0 x 2 + 1600 x 2 = 4.00 m

You will find the result in the Cost breakdown (see image below)

Unfortunately the “Rod Extn Below” is not taken into consideration when calculating the rod length for either method.(see image below)

Note: The seismic rod options are also not taken into consideration when calculating the rod length for either method. (see image below)

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