Beginners cut every part to its exact final dimension. Professionals don't. They oversize most parts on the table saw, then trim to final size on a router, jointer, or table saw with a fresh blade.
This sounds wasteful - and on the optimizer screen it looks wasteful - but it's how cabinet shops produce work that actually fits together. Here's when to oversize parts in your cut list, and by how much.
Why oversize at all?
Three reasons:
Recovery from cutting error. Saw blades drift. Fences move. A part cut at exactly 564mm on a slightly out-of-square saw is now 563.7mm on one end and 564.4mm on the other. Oversize by 3mm, then trim with a flush-trim bit on a router using a known-square reference and you get a true 564.0mm part.
Account for joinery. A part with a dado joint needs to be sized including the depth of the dado. A part with iron-on edge banding needs to be sized minus the banding thickness on each banded edge. Oversizing during the cut and trimming after assembly compensates.
Match tolerance to the joint. Some joints care about a 0.2mm tolerance (drawer slides). Some couldn't care less if you're 5mm off (wall cleats). Oversize generously where tolerance doesn't matter; oversize precisely (and trim precisely) where it does.
Typical oversize amounts
| Part type | Oversize | Trim method |
|---|---|---|
| Cabinet doors (inset) | 6mm width, 6mm height | Router flush trim, then size to 3mm reveal |
| Cabinet doors (overlay) | 3mm each side | Router flush trim |
| Drawer fronts | 6mm width, 6mm height | Router or table saw |
| Drawer boxes | 1mm length and width | Trim on table saw with sled |
| Cabinet sides (frameless) | 1mm length, 0mm width | Trim length on miter saw |
| Shelves (between fixed sides) | exact width, 1mm shorter than opening | Sand to fit |
| Tops | 6-12mm overhang built into final size | Cut to overhang dim, no trim |
| Backs (rabbeted) | 1mm undersize on rabbet faces | No trim |
| Wall cleats | 6mm undersize | No trim, gap is hidden |
When NOT to oversize
When the cut is the final cut. If you're using a track saw with a known-good blade against a long fence, your cut might be more accurate than your router setup. Don't oversize for the sake of it.
When material is precious. Hardwood plywood at $90/sheet, walnut veneer panels, brass or copper sheet - every mm of oversize costs money. Make accurate cuts and skip the trim step.
When the part is symmetric and rotation-tolerant. Backs, blocking, paint-grade interiors. Just cut to size.
When trim takes longer than re-cutting. A 30-second router pass costs you more than re-cutting a $5 part. Decide based on your time vs material trade-off.
How to enter oversized parts in a cut list optimizer
Two approaches:
Option A: Enter oversize dimensions in the cut list. Add the oversize amount to every part before entering. Pro: the optimizer respects the real physical sizes you'll cut. Con: you have to track which parts are which size at glue-up.
Option B: Enter final dimensions, oversize at the saw. Note next to each part what size you'll actually cut. Pro: cut list matches the final part list. Con: the optimizer's layout may not be optimal for the bigger physical parts.
For most projects, Option B is correct. The optimizer's layout decisions are based on relative sizes, not absolute, and the few mm of difference doesn't change which parts pack well together. Save Option A for tight builds where you absolutely need the optimizer to model real cutting dimensions.
The "trim allowance" trick
Some woodworkers add a single line at the top of every cut list: "Add 3mm to all dimensions for trim." Then they enter parts at final size and mentally adjust at the saw. This works fine on small projects with a few part types. On a 40-part kitchen cabinet job, you'll lose track. Use Option A or Option B explicitly instead.
Edge banding math
If you're applying iron-on edge banding (typically 0.5mm thick) to two long edges of a part:
- Cut the part 1mm under final width (0.5mm × 2 banded edges).
- Apply banding.
- Trim flush.
Final part = exactly your design dimension. Easy to get wrong if you forget which edges are banded - annotate every banded edge in your cut list.
The cabinet-shop default
If you ever take a cut list to a commercial cabinet shop, they'll typically add:
- 6mm to door widths and heights (for inset doors with reveal)
- 3mm to drawer fronts (for fitting)
- 1mm to cabinet sides (for trim square)
- Edge banding allowance to all visible edges
This is their standard "cabinet shop overhead" - the cost of buildable parts that fit the design. If you want shop-quality work in your own shop, build the same overhead into your cut lists.
Bottom line
Oversize 1-6mm depending on the joint and the trim method. Decide before you sit down to optimize, so the cut list reflects how you actually plan to work. The optimizer can't read your mind, but it can give you a clean layout once you've made the call.
Try the cut list calculator and add a few mm to your part dimensions if you plan to trim. Or load a project template that's already sized for typical shop tolerances.
Related: How Saw Kerf Affects Waste · Plywood Grades Explained