Decypering Acrylic Measurements

[R. A. Mitchell]

I'm looking at different vendors for sheet acrylic to figure pricing to quote a couple of jobs. What I have noticed is that there is a big price discrepancy with acrylic sheet depending upon the measurements for purchase.

If you look at an industrial supplier like McMaster Carr, they carry acrylic in a variety of different thicknesses. If you buy .118 cast acrylic instead of 1/8", the savings are disproportionate to the price changes among various other thicknesses. In other words, they seem to charge a premium for 1/8" ($17.48 for 24x12) over .118" acrylic ($9.67 for 24x12) which, because of tolerances of thickness, may very well be 1/8". Same thing holds for .236" acrylic and 1/4". And I also noticed that the extruded acrylic is only sold in the thicknesses that correspond to the decimal expressions, not even fractions (those are only sold in bars and rods).

Anyone know why the prices are disproportionately higher for fractional thicknesses of acrylic as opposed to the thicknesses expressed by decimal? Given the pretty wide tolerances in sheet acrylic thickness, does anyone know of a good reason to stick with the fractional widths over the decimal widths?

p.s. - I caught the typo in the subject after I posted, but I can't edit the title to correct it. Sorry.

[Margaret Turco]

I'm guessing that the decimal thicknesses (metric equivalents) are all imported, so typically less expensive.

[Mike Mackenzie]

I personally would not buy any acrylic from McMaster. There are plenty of Plastic suppliers that would be much cheaper.

[Mike Null]

I agree with Mike. A local supplier may save you money on the price but certainly on shipping.

[Doug Griffith]

I'm curious if McMaster's more expensive fractional sizes are accurate within a few thousandths sheet to sheet and corner to corner.

[Joe Pelonio]

McMaster is more of an industrial supply. When you ask for a certain thickness it's a lot more likely to be what you asked for. Most other vendors, including 4-5 local ones I use, may sell you .236 or 6mm as 1/4". It's almost like buying a 2x4, it's not 2"x4". For most applications it doesn't matter, but I have recently had problems with jobs that required a specific thickness.

[R. A. Mitchell]

This is more along the lines of my question. While I appreciate everyone's encouragement to seek out a local vendor, I'm still trying to figure out why such a large price discrepancy exists between very similar measurements. Is it an industry thing, or a vendor thing? I suspected there was an issue with metric equivalents, but that doesn't explain the difference in price. My assumption is that the fractional acrylics would be the most popular and therefore the least costly because of economies of scale, but that doesn't seem to be what the market reflects.

[Dan Hintz]

While I cannot say with any certainty, you may be on to something about the difference between metric and standard being due to foreign-made and domestic-made materials. Most foreign-made will tend towards metric, hence the decimal measurement in mils and possibly the reason for being less expensive (domestic manufacturing of materials tends to be more expensive, usually due to EPA regulations, etc.).

[Doug Griffith]

If the McMaster fractional acrylic holds tight tolerances then the higher price could be due to a more precision (and time consuming) manufacturing process by their vendor.

[Richard Rumancik]

Recently a customer inquired about having a part made from .250" acrylic instead of 6 mm (.236"). When I researched it I found that there was very little acrylic available at all in fractional measurements. Most of the world's acrylic seems to be metric from what I saw. I recall seeing a few lines in limited colors in fractional sizes. However, note that the tolerances can be large, so that a "low" 1/4"-thick sheet could end up being close to or overlap into the 6mm size range.

My assumption is that if someone is selling true fractional sizes, the price reflects the smaller quantity that is manufactured at this nominal size.

As Joe mentioned, a lot of suppliers, particularly hardware-store types, will call 6mm material 1/4". Their customers might not understand metric and perhaps really don't care about the difference between .236 and .250.