Calculating the Weight of metals

I was working on a quotation involving Control and Relay panels when my client had some major issues with the fabrication rates.

I enquired my fabricator for the break -up of aluminium and steel components of the panel. He gave me certain rates and gave me a weight calculation assuming a certain weight per meter. I being an engineer could have calculated the weight myself knowing the density f aluminium is 2.8 grams per cubic centimeter. Instead I worked upon a rate based on his calculations and faced some embarrassment in front of the client. And that too he is in the aluminium business so I cant claim ignorance and get away.

So for all the friends who need to calculate the amount of metal which goes into a making a product...

Take the size: eg: 100mm * 10 mm (width * thickness)
Take the length : eg: 3000mm (3 mtr long)
Metal : Aluminium
Density : 2.6- 2.8 grams per cubic cm

Now converting all to centimeters and multiplying as follows -
(100 mm* 10mm* 3000mm * 2.7gms/cm)
(10cm* 1cm* 300cm* 2.7gms/cm) / 1000
8100 / 1000
8.1 kg
We have considered 3000mm / 3 mtr so per meter we get 2.7 kg
100*10 flat of aluminium weighs 2.7kg per meter.

similarly,
Given the size and length of the materials needed, it is simple to calculate the total weight required.

I would warn you that a lot of websites, good ones, carry wrong information about the weights per cubic centimeter of well known metals/alloys. I would urge you to look into the information section of metals.org / have a engineering conversion table for steel and other materials.

Why is it important to know the weight?
Most of us who have bought steel or copper or any other metal will know that the dealer will be billing it to us in terms of the weight regardless of the quantity. And usually our clients will be given us rates for quantity rather than weight. So its very important for us to know the conversion between qty and weight.
Eg: ITEM SIZE UNITS QTY RATE TOTAL
Clients --> Copper 50*6 mtrs 10 1174 11740
Supplier--> Copper 50*6 Kgs 26.7 440 11748

Supposing our conversion was wrong and we had estimated the weight on the lesser side then, the supplier is safe because regardless of the weight per meter he will bill as per actual weight. The client is safe because we will bill him for length and does not care about the weight. So in case weight per meter increases the impact will be felt only by us. So its important to calculate carefully.