Engineering · Cost
Tolerance vs cost — the ladder.
Each step tighter on tolerance multiplies cost — and the multiplier is steeper than most engineers expect. Below: the eight-tier ladder we use when reviewing customer drawings, with typical processes and example applications. Use it before tightening a tolerance — the question to ask is “does the part actually need this?”
Interactive Reference
Tolerance Cost Curve Analyzer
Select a tolerance tier below to analyze how tight dimensional callouts affect part cost, scrap risk, and quality control (QC) inspection workloads. The curve visually demonstrates the steep cost penalty of high-precision machining.
Can be run on standard manual or 3-axis mills with minimum setup overhead.
| Tier | Tolerance | Cost vs baseline | Process | Typical features |
|---|---|---|---|---|
| Tier 1 | 0.030″ (0.75 mm) | 1.0× | Standard milling, single-pass turning, sawing | Bracket envelopes, weldment blanks, non-mating clearances |
| Tier 2 | 0.010″ (0.25 mm) | 1.2× | Standard CNC, no special tooling | Most general structural features, clearance holes, blank dimensions |
| Tier 3 | 0.005″ (0.13 mm) | 1.4× | Standard CNC with tighter QC | Mounting bores, dowel-pin holes (clearance), fastener spotfaces |
| Tier 4 | 0.002″ (0.05 mm) | 2.0× | Precision CNC, in-process probing | Bearing fits, sliding fits, locating features, mating surfaces |
| Tier 5 | 0.001″ (0.025 mm) | 3.0× | Glass-scale machine, CMM verification | Precision bushing IDs, locating dowel holes, optical mounting interfaces |
| Tier 6 | 0.0005″ (0.013 mm) | 5.0× | Makino-class precision mill, careful thermal management | Press-fit interfaces, gauge surfaces, metrology fixtures |
| Tier 7 | 0.0002″ (0.005 mm) | 8–10× | Wire EDM or grinding for finishing | Bearing races, optical alignment surfaces, gauge masters |
| Tier 8 | 0.0001″ (0.0025 mm) | 15–25× | Wire EDM, jig grinding, lapping | Tool-and-die work, ultra-precision metrology, quantum/cryo flexures |
Why the cost climbs so fast
It’s not just the cut.
- Tighter tolerance forces tighter machine selection.
A 0.005″ feature runs on any mill. A 0.0005″ feature needs a Makino-class precision machine with glass scales — different machine, different rate, different schedule.
- Inspection time scales with tolerance.
0.005″ gets a quick gauge check. 0.0001″ gets full CMM measurement, environmental control, and statistical process verification. The inspection load alone can multiply per-part cost.
- Yield drops at the tight end.
0.001″ might run 99% yield on a good day. 0.0001″ routinely runs 70–85% yield with a 2× cost penalty just to absorb the scrap rate. We build that scrap allowance into the quote.
- Setup time grows with tolerance.
A loose-tolerance bracket sets up in 20 minutes. A 0.0002″ gauge surface might need 2 hours of setup, validation, thermal stabilization, and trial cuts before production starts.
- Process changes — sometimes you have to.
Below 0.0002″ on inside corners, milling can’t physically hold the spec. Wire EDM is the only option, and EDM time is more expensive per inch than milling. Same for 0.0001″ precision flatness — grinding becomes mandatory.
Practical guidance
Three rules for not overspending on tolerance.
- 1. Tolerance only what mates or measures.
Bearing fits, alignment surfaces, sealing surfaces — those need precision. Edges of a bracket, hole locations far from a datum, cosmetic features — those don’t. Apply tight tolerance only where it matters functionally.
- 2. Use ISO 2768 or default-tolerance blocks.
Specifying ±0.005″ on every dimension when only three need it triples your cost vs. a default-tolerance block (e.g., ISO 2768-medium) with explicit tighter tolerance only on critical features.
- 3. Specify GD&T relative to actual datums.
A 0.001″ positional tolerance referenced to the right datums is much cheaper than 0.001″ on each X/Y/Z dimension. GD&T allows the machinist to optimize stack-up; per-axis tolerance forces them to hit each independently.
Keep exploring
Related tools & references
Achievable tolerances by process and how to call them out.
Worst-case and RSS analysis across a dimension chain.
ISO 286 fit classes for mating holes and shafts.
Find cost-driving callouts before a drawing is released.
See how tolerance and finish choices roll into piece price.
The finish side of the same cost trade-offs.
Technically reviewed by the True Precision Machining engineering team · Last reviewed June 2026
Standards referenced: ASME Y14.5-2018, ISO 2768
Want a DFM tolerance review on your drawing?
Send the drawing — we'll walk it for tolerance choices that drive cost and flag where loosening callouts would save real money without affecting function.
Quotes in 24 hours