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How to Convert Pounds to Inches for Welding Wire

It is almost impossible to do a welding job without knowing how much welding wire you will need. While many welders know how to calculate the weight of wire required for a weld, it's just as important to be able to work out the length of wire needed to produce this weight as this allows you to get the the feed rate correct while you weld. Performing this calculation mathematically, rather than by luck or judgment, saves you time and resources and improves the quality of your welding.

Calculate the amount of wire you need with a few simple equations.
  1. Find the size of the wire written on the drum or spool. Welding wire is usually described using its diameter in fractions of an inch. Halve this number to get the radius, then multiply the result by itself to get the radius squared.

  2. Measure the wire in fractions of an inch if you cannot find the diameter written down. Make sure that the end of the wire is cut flat and makes a perfectly round circle, and measure across the widest point from one side to the other. Halve your measurement to get the radius, then multiply the radius by itself to get the radius squared.

  3. Multiply the radius squared by pi if you have a scientific calculator that has this button on it. If not, multiply the radius squared by 3.1416. This gives you the area of the face as well as the volume in cubic inches of an inch of wire. This is because the volume equals the area of the face multiplied by the length of the wire; if you want the volume of one inch of wire, the area of the face multiplied by one leaves the answer unchanged.

  4. Multiply the volume by 0.0245, which is the weight in lbs. of a cubic inch of solid steel wire. This gives you the weight of an inch of the size of wire you are using.

  5. Divide the weight of welding material you need by the weight per inch of wire to give you how many inches of wire you need. This only applies to solid steel wire -- if you are using metal or flux cored wire multiply this result by 1.05 to give you an estimate of the amount of wire you need.