Coil and Wire Rod Weight and Its Calculation Formula; The Same Rebar Rule

The good news for anyone who has worked with rebar is this: the weight of coil and wire rod is calculated using exactly the same familiar rebar formula. Since both have round cross-sections, the rule of diameter squared divided by ۱۶۲ is the same for both.

The Weight Formula, the Same Round-Section Rule

The weight of each meter of coil or wire rod in kilograms equals the diameter (in millimeters) squared, divided by ۱۶۲. This is the same formula used for rebar, because both are round steel products with a density of ۷.۸۵. To calculate the total weight of a coil, multiply the weight per meter by the total length of the coil.

Coil weight has a squared relationship with wire rod diameter; in other words, a small change in diameter has a major effect on the total weight.

Weight Table for Several Commonly Used Sizes

Why the Squared Relationship Matters

Because the diameter is squared in the formula, a small change in diameter has a major effect on the total weight of the coil. If a coil that should be ۶.۵ millimeters is actually ۶.۲, the weight difference in a coil weighing several tons becomes significant. This is why checking the diameter and controlling coil weight are important for buyers.

Before settlement, estimate the theoretical weight of the coil using the formula and compare it with the weighbridge weight; a large and downward discrepancy is a sign of a smaller-than-specified diameter or underweight.

A Practical Point About Weighing Coils

Unlike individual bars, which are simple to weigh one by one, accurately weighing a complex coil requires a scale that shows the entire coil's weight at once, rather than an estimate based on its apparent diameter. If direct weighing is not possible, measure the coil's approximate length from its circumference and calculate it using the formula, then compare the result with the declared weight.