Aren’t sheet metal thickness measurements absolutely maddening?
Copper thickness gets measured in ounce. Steel and stainless steel get measured in gauge. Aluminum is measured in inch. Ok. Technically they call it decimal measurements. So is titanium. But since aluminum is weaker than titanium, you’d specify a differing decimal thickness for each metal for the same application. Zinc is measured in millimeter.
Standard sheet sizes are never the same for sheet metal either. Some only come in metric. Some in metric and Imperial simultaneously and the size options are totally dependent on what you’re ordering.
You might have noticed that if you asked us to quote for a system like diamond shingles in both zinc and copper, we’d recommend a slight size difference of shingle between the two metals in order to make the most efficient use of material and to keep costs down. This is because of the way these materials come from the mills.
Why is this randomness so pervasive? Though it would be utopia if there were a more standard system, we can blame things on history, tradition and origin and usage.
Zinc for architectural metals is almost exclusively produced in Europe. It’s popular and cheap over there. 85% of all metal roofs in Paris are zinc! Of course then it makes sense that zinc would come in both metric thickness and dimension options.
Semi-precious copper is an indexed metal like gold. Therefore, it’s been historically classified in much the same way. Let’s veer off track for a moment and discuss troy ounces vs. avoirdupois ounces, just because it’s interesting and history is fun!
If you were to start buying and selling gold, silver, and other precious metals, you might be surprised to find that a different unit of measure is used to weigh precious metals. Typically, these metals are weighed using the troy weight system as opposed to the more familiar way that we measure other goods such as sugar or grains.
Why are troy ounces important?
If you buy a one ounce gold coin and place it on a standard grocery-store scale, you would find that it’s approximately 10% heavier than an ounce of beef. The two measures are not the same. Many people don’t realize this, which is why they often fall victim to sellers who try to boost the value of their products by simply listing them in ounces. For example, a seller could claim that a precious metal weighs 100 ounces, but you would be losing around 10% of its value because it actually only weighs 90 troy ounces.
It may seem like an unnecessarily complicated system, but there are good reasons that precious metals have their own unit of measure. The troy was retained as the standard unit of measurement over the avoirdupois ounce to ensure purity standards and other common measures remained consistent over time. Avoirdupois? We’re getting to that…
History of the troy ounce:
No one knows for sure when and where the troy weight system was born, but the most commonly held explanation is that its name is derived from Troyes, a trade market in France. Merchants came from all over the world to buy and sell goods, so a standardized weight system would have made doing business much easier. Later, many places in Europe came up with their own version of the troy ounce, but the French troy is believed to be the system most closely related to the one that we use today.
If we care to trace the origins of the troy even further back, we could look to the Roman monetary system. Romans used bronze bars as currency, and the bar that was equal to one pound today was referred to as an “aes grave.” A twelfth of that was called an “uncia,” or ounce. Today, a troy ounce is a twelfth of a troy pound.
The troy ounce today:
Prior to the adoption of the metric system, French-born King Henry II of England adjusted the British coinage system to be more reflective of the French troy system. The system was adjusted periodically, but troy weights as we know them today were first used in England in the 1400s. By 1527, the troy ounce became the official standard measurement for gold and silver in Britain, and the U.S. finally followed suit in 1828.
Today, the troy ounce is the only unit of measure of the troy weights system that we use. Just like the traders of Troyes in France, buyers and sellers today need a good, standardized form of measurement for precious metals.
Troy ounces vs. avoirdupois ounces:
So, how is an ounce of gold different from an ounce of sugar? While the gold is measured by troy ounces, goods such as sugar or other items are measured using avoirdupois ounces. The name might sound completely strange to you, but the avoirdupois is the unit of measure that we use to weigh almost everything else other than precious metals. The scales at the grocery store and the scales in your bathroom weigh things in avoirdupois ounces. Because the avoirdupois ounce is so common, we simply refer to it as “ounces.”
Obviously, then, a troy ounce is a bit heavier than a regular ounce. One regular ounce is 28.35 grams, while a troy ounce is 31.1 grams. The weights are close, but the difference becomes very noticeable when you’re dealing in larger quantities of precious metals.
Here is where it can become confusing. Recall how we said that the troy system was indirectly derived from the Roman monetary system, using 12 troy ounces to make up one troy pound. This makes a troy pound lighter than a regular pound, even though troy ounces are heavier. This is only possible because fewer troy ounces are needed to make a pound — 12 as opposed to 16 ounces for a regular pound.
You may also want to take note that copper, being a base metal, is weighed using the avoirdupois ounce. Be sure to keep this in mind.
As you can see, it’s important that any buyer of precious metals has a thorough understanding of the ounce if he or she wants to safely and smartly navigate the precious architectural metals market.
Now, we move from ounce to gauge:
How did we start measuring in gauge?
When the first sheet metal rolling mills were established in North America, most manufacturers offered products in different thicknesses that were defined by their own standards. Manufacturers’ standards were usually related to weight, and sometimes related to existing wire gauge diameters. As you can imagine, thicknesses differed for each manufacturer’s gauge standard. Eventually, the most powerful manufacturer’s standard for each industry became accepted, but since manufacturers tended to specialize in a particular industry or type of metal, separate standards evolved for different materials.
Today when you see gauge numbers, which usually run from about 7 to 30, the same gauge number may represent different thicknesses depending on which standard is being followed, and there are many!
What gauge is thicker?
Generally, as gauge increases, the thickness of the metal decreases. In other words, a 24 gauge sheet of galvanized steel is actually thicker than a 26 gauge sheet of galvanized steel. The inverse relationship between thickness and gauge probably stems from early wire and sheet metal manufacturing processes. Each time the metal passes through a die, it becomes thinner, so gauges at one time equated to the number of times a metal passed through a die.
The trouble comes in comparing metals that follow different sheet metal gauge standards. That’s because the same gauge number (say, 30 gauge) differs in thickness depending on the variety of metal. Example: 30 gauge galvanized steel is defined as thicker than 30 gauge uncoated steel. So even gauge is misleading.
Whether you’re deciding which sheet metal is most appropriate for an application, or comparing two metals with different gauge standards, decimal thickness is a much more accurate way of measuring that is not open to interpretation. Trouble is, as we have discussed, you can’t order everything in decimal and conversions based on relatively capricious measurements could make for dubious equivalencies when not properly accounted.
The tin foil hat conspiracy theorists that lie deep within us would say that all this randomness by the metals industry in its current state is meant categorically to cause confusion thereby enabling sellers to capitalize on an overwhelmed buyer and persuade them to purchase more / thicker material than is truly necessary to properly accomplish their project. Though certainly that is not a full truth and we don’t intend to perpetuate this fable, the fact of the matter is, the current bewildering system could very much result in the same outcome.
We get it. When we first moved to the U.S. from Europe, our heads about exploded with having to calculate Imperial measurements on top of everything else. It’s crazy. And there’s not really a better word for it.
If you are completely confused and need to compare systems, just convert them to metric. That’s really the easiest hack to determine thickness comparisons.
But whatever you do, don’t get taken and don’t get overwhelmed. We know the architectural metals industry backwards and forwards. We can calculate precisely what you need and help you stay on track, on budget and with your wits still intact.
If you’re not familiar with how to plan and calculate architectural metals, we’ll be delighted to help, and even if you do, we’ll make certain you get the best value out of your materials as possible. Call today and we’ll get to work for you!
801-462-5264
