The thickness of a copper pan determines a great deal not only about its cooking performance but also its value. Measuring it can be tricky, and I have some suggestions that I hope are helpful.
Generally speaking, the newer the pot, the more likely it is to have a consistent thickness throughout, and the fewer thickness measurements you will need. The older the pot, the more measurements you will likely need in order to come to an assessment of its effective thickness.
You can take some time with a pot that you have in your possession. But if you’re working with an eBay or Etsy seller, you may have to work with the information they provide — or if you’re lucky, you can ask them to measure for you. I offer these suggestions to help you make the most of whatever opportunity you have.
Start by taking a good look at the pot to assess how (and if possible, when) it was manufactured.
A modern-era pot — one made after World War II — was most likely machine-formed from a piece of copper sheet. These modern manufacturing processes produce beautifully symmetrical and balanced pots of uniform thickness throughout, so for these pots, a single measurement at the rim will likely be accurate for the entire pot.
A hand-raised pot is made from a flat sheet of copper that has been hammered into shape. These pans are often thicker in the base than at the rim, so the effective thickness is best assessed as a combination of both measurements. This technique is more prevalent in truly antique pots from the 19th century and earlier before machinery was invented to assist with cutting and shaping tasks, but some modern ateliers continue to hand-raise pots.
A dovetailed or soldered pot is assembled from individual sheets that are joined together. In general, each section has the same thickness, but it’s possible that really big old pieces like rondeaux could be given thicker bases than sides for structural integrity. You have to use your judgement when assessing dovetailed pieces to decide whether you need to take multiple measurements.
A smooth-finish pot is more likely to be of modern construction, and to have a consistent thickness around the entire rim. For this type of pot, it’s sufficient to measure the pot once at the rim.
A hammered-finish pot will have tiny variations in thickness according to the peaks and valleys of the hammer marks. The best measurement strategy in this case is to take multiple measurements and use the average.
Where and how you measure a pot can affect the measurement, so it’s important to do it properly.
Use millimeters, not inches. In terms of copper cookware performance, the difference between 2mm and 3mm is significant — but that same increment is just .04 inch, too fine for most household rulers or tape measures. Find a metric ruler or tape measure, or better yet, a set of calipers that can read to a tenth of a millimeter or better.
Measure straight across the rim. Lay the ruler or tape measure flat over the top of the pot and ensure it runs exactly over the center of the pot. If you’re using a caliper, look down from above to ensure you’re not angling it up or down or sideways.
Measure in multiple locations. Modern-era machine-shaped pots tend to have consistent thickness throughout, but older pots can vary around the rim and from the rim to the base. If the piece you are measuring has a hammered finish, you will want to find the average thickness over multiple measurements in different spots.
Measure at and below the rim. If you have calipers, take a measurement right at the rim, and then again as low as you can below it. As above, modern machine-made pots tend to be consistent, but older hand-hammered pots thin out towards the rim.
Measure below a flared or bias-cut rim. Pans with “pouring lips” flare out at the rim and are tapered or cut on the bias, which won’t yield a true thickness value. If you have calipers, measure below the flared area. If you don’t have calipers, measure the rim and make your best guess as to how much to subtract to get an accurate estimate of the pan wall.
If you’re using calipers, use the lowest value you can acquire. Your goal is to measure the shortest straight line across the thickness of the pan wall, which means capturing the shortest distance between the caliper’s tips. You may need to wiggle the calipers a little until you find that smallest measurement.
If you’re looking at an antique pot, measure the base thickness as well. For many antique pots hand-raised from thick copper sheet stock, the sidewalls may be thinner than the base, and so sidewall measurements would not reflect the pan’s effective thickness. This can be challenging to do, however — I don’t have calipers big enough to do this and so I use rulers, and I’ll show you the technique I use below.
The most useful tool for measuring pan thickness is a set of calipers. There are many types and you can spend as much money as you wish, but you don’t need an expensive industrial one for this task. I own two, a digital caliper I bought for US$10 from Amazon, and a dial caliper I bought for US$20 from Ebay. Of the two, I prefer the dial caliper shown on the right.
The problem with the digital caliper is that its broad flat piston can produce an inaccurate measurement if not positioned correctly. Any curvature or irregularity in the measuring spot, or any angle introduced by the user, will distort the caliper’s reading. I find that the dial caliper’s needle-point prongs produce a more precise measurement that’s less prone to distortion.
If you want to find one like it, this caliper is categorized as a “dental dial caliper.” As I mention above, it was just US$20 from eBay, and it came with a lovely plastic case.
Rulers and tape measures
A good ruler or tape measure with metric measurements can measure pan thickness at the rim. Just make sure you measure directly across the rim and do not introduce a slant that could inflate the measurement.
You can also use rulers to measure the thickness of the base of the pot. You’ll need a ruler (or measuring tape) and some kind of rigid flat object to lay across the rim of the pot as a reference point. (You don’t need two rulers for this — one ruler or measuring tape will do.)
The photo below is measuring the base thickness of an antique Dehillerin Windsor. I’ve laid a level (the rigid flat object) across the rim of the pan to serve as the reference point. The black ruler is resting against the tabletop, and the distance to the reference point is 71mm. The red ruler is resting on the inside base of the pan, and the distance to the reference point is 67mm. The difference between the measurements of the two rulers is 4mm — the thickness of the base of the pot.
If you don’t have your measuring tools with you, you can use pocket change to estimate the thickness of a pan. Here are the thicknesses of some common coins.
|US coin||Thickness in mm|
|Euro coin||Thickness in mm|
|1, 2, and 5c||1.67mm|
To use this method, hold one or more coins up to the rim and compare their thickness. This is not a precise method, of course, but it’s useful if you come across a pot or pan and want to estimate its thickness.
In the example below, I’m holding two US pennies against the rim of the Windsor. Near the handle, the rim is two pennies thick — about 3mm. But this is an antique pot, hand-raised, and the rim is uneven. On the opposite point on the rim, it’s about one penny thick, or about 1.5mm.
French copper pots can be distinguished across three thickness break points: less than 2mm; 2 to 3mm; and 3mm or more. In general, the value (and price) of a piece of copper increases as its thickness increases.
Here are some good coin combinations that come close to the copper thickness reference points.
|To measure…||With US coins||With euro coins|
|1.5 mm||One penny (1.55mm)||One 1, 2, or 5c (1.67mm)|
|2 mm||One nickel (1.95mm)||One 10c (1.93mm)|
|2.5 mm||Two dimes (2.7mm total)||One 50c (2.38mm)|
|3 mm||One penny + one dime (2.9mm total), or one dime + one quarter (3.1mm total)||Two 1, 2, or 5c (3.34mm total)|
|3.5 mm||Two quarters (3.5mm total)||One 1, 2, or 5c + one 10c (3.6mm total)|
|4 mm||Two nickels (3.9mm total)||Two 10c (3.9mm total)|
As you grow your copper collection you will come to understand and appreciate how each piece cooks for you, and how thickness is an important component of this. I hope this information helps you to quantify what you already sense about the copper you have as well as to understand what you’re buying.