Nominal vs. Exact Sizes: Reading Acrylic Dimensions and Tolerances
Acrylic sheet is manufactured and sold to nominalsizes — the labeled, rounded figure, not a guaranteed exact measurement. A sheet sold as 1/4″ thick or 12″ × 12″ will be very close to those numbers, but every acrylic sheet carries a small manufacturing tolerance. Knowing the difference avoids surprises when a piece has to fit a frame, channel, or opening.
Thickness is nominal
Acrylic thickness is named by its nominal gauge (e.g. 1/8″, 1/4″, 1/2″). Actual thickness runs to roughly ±10% of the nominal thickness and can vary across a sheet and from lot to lot. If your design relies on a precise thickness (press-fit slots, stacked layers, machined pockets), plan for that variation and test-fit before committing to a large run.
Sheet (stock-size) dimensions are nominal
When you order a stock size without cut-to-size, you receive a sheet at that nominal width and height. Sheet length and width carry a tolerance of approximately ±1/8″. The edges are clean saw cuts, square but not optically finished unless you add polished edges.
Saw-cut pieces
When you add the cut-to-size option and specify finished dimensions, the piece is saw-cut to approximately ±1/16″ to ±1/8″ — all of our cutting is saw-cut. Your finished dimensions must be smaller than the stock size you selected in both width and height — we cut down from the sheet you order, we do not add material.
Tolerances at a glance
| Dimension | Tolerance |
|---|---|
| Acrylic sheet thickness | ±10% of nominal thickness |
| Sheet length & width | approximately ±1/8″ |
| Saw-cut pieces (all cutting) | approximately ±1/16″ – ±1/8″ |
Ordering when exact size matters
If a piece must drop into a tight opening, design in a little clearance. A common approach is to order cut-to-size a small amount under the opening (for example, target 1/16″ smaller than the gap) so normal tolerance plus the fit allowance still lets the piece seat. For glazing held in a channel, leave room for expansion — acrylic expands and contracts more than glass with temperature.