-It helps you to get a general idea of the cost of each purchase.
-It helps you to bring a big enough vehicle to get your stock home.
-If you are making a product that has to be shipped
you can find out ahead of time how much the shipping cost will add to the project.
-If you are making a product that has to be lugged up a flight of stairs for installation,
you need to know how many people it will take to get it there without buggering up somebody's back or the walls of the
-If the product is VERY heavy, you will have to know how big a crane or other lifting device will be needed.
-If you have even a general idea of the weight of your order, you can avoid getting ripped off by a devious or simply sloppy
-There are tables that you can use, and we should all have them. They usually come in booklet form. They usually list
the wieght per foot for most common stock sizes.
Most steel suppliers give them away. Just ask. One Example of A Website with charts
Okay, I am getting a little wacky, here, but hear me out on this one!:
1. Use what I call "The Cannibalism of numbers" to remember how much steel weighs. Fact: Most steel weighs about 489 pounds per cubic foot.
That's nice, but how often do you buy steel by the cubic foot?
Well, not very often, if you are anything like me. BUT!!! I do buy bars that may be 1 inch square. Or 1/2 inch square.
(Unfortunately, you metric blokes are going to have to convert as needed)
Annyway, the "Cannibalism of numbers" is when "two ate three" (283)--ha-ha-
One cubic inch of steel weighs 0.283 pounds. So, a 1" square piece of steel 1 foot long weighs (1 X 1 X 12 X .283) or about 3.4 pounds.
That's it! You use simple arithmetic to arrive at the volume of the stock you are buying and multiply that number by 0.283 to get its
weight in pounds.
"Okay", you say; that still takes a lot of brain power to do.
Maybe so. But, if you don't require high accuracy, simply round 0.283 down to 0.25 or 1/4 of a pound. Now, you can simply divide the volume of the stock
(in cubic inches) by 4 and you have the approximate weight in pounds! What could be simpler?
Well, maybe this could be a simpler method for you. Depends upon that way your personal brain works:
2. Fact: A 12" X 12" X 1/4" thick piece of steel weighs almost exactly 10 pounds.
Just translate whatever pieces you need into handy multiples of this to estimate approximate weight.
Here's a simple example: You want to buy a bar that is 1/4" thick, 1" wide and 12 feet long. How much does it weigh?
Answer: Simply imagine the piece as it relates to the above "fact": Instead of being 12" square, your bar is made by
slicing that 12" wide bar into 12 pieces that are one inch wide. Now it is 12 feet long!
How much does it weigh? Ans: 10 pounds.
One other example:
Suppose you want to buy 12 feet of 1/2" square bar.
Imagine that you sliced it down the middle so you had 2 bars that were 1/2" X 1/4" X 12 feet long.
If you laid the pieces side-by-side, you would have a bar that is 1 inch wide by 1/4" thick, by 12 feet long.
Again, the weight would be 10 pounds.
We all know that the area of a circle is equal to pi times the radius of the circle squared.
Multiplying the area of the cross section by the length, gives us the volume, incubic inches. Once we have the volume, we can apply the
"cannibalism of numbers" from the above examples to find the weight of our stock.
BUT!, there's an easier way!.
Fact: The area of the largest circle that can be drawn inside a given square is 78.43 percent of the area of that square.
So, you can simply take the square of the cross section of the round bar you want to buy, take 80% of that, multiply that
number by the length in inches to get the volume. Then take 1/4 of the volume, and you have the weight in pounds!
Example: You want to buy a 1" diameter bar that is 100 inches long.
One X one is one. Eighty percent of one times 100 inches equals 80 (cubic inches). Eighty divided by 4 equals 20 pounds.
That's all there is to it!
Most other shapes can be broken down into units that can be worked with these ideas. For example, an extruded piece of rectangular
tubing 4 X 6 inches, with 1/2" wall: It is simply the area of a 4 X 6 bar minus the area of a 3 X 5 bar.
Remember here, we are estimating, so if the parts are going up in a rocket ship, better to use the tables.
-I use the shipbuilding assumption that steel a foot square and an inch thick weighs 40 pounds. 1/2" steel is 20 pound plate, 1/4" is 10 pound plate, etc.
-Rather than using formulas for pipe and tubing I measure the wall and wrap the tape around the outside.
-For channel I figure 3" as 4 Lbs per foot and 4" as 5 Lbs, which aren't exact but are close enough when I'm out wading through the mud and the calculator and Manual of Steel Construction are back safe in the vehicle. I keep a 50 Lb fishing scale and loop sling in the car for smaller stuff like angle.