Tolerance Stack-Up Calculator
Upload your drawing or describe your dimension chain. Get worst-case, RSS, and Monte Carlo stack-up results, violation flags, and specific corrective tolerance recommendations, in seconds.
Run Your Stack-Up FreeNo credit card required · Free plan includes 10 analyses/day
No confusion, no setup
Exactly what happens, in order
Describe the dimension chain
List each nominal dimension and its tolerance, or upload the drawing. No spreadsheet setup, no formulas to write.
Get worst-case, RSS, and Monte Carlo
See the gap range under worst-case (guarantees 100% yield), RSS (statistical, more economical), and a Monte Carlo simulation for non-normal distributions, with a pass/fail against your functional requirement.
See exactly what to tighten
A sensitivity ranking shows which dimension controls the most variation, with a specific tolerance change that fixes a failing stack.
Real output, not a mockup
This is what you get back
From the prompt: "Bearing assembly, housing bore 20.00 ±0.05mm, pin OD 19.85 ±0.03mm, sleeve wall 0.05 ±0.01mm, gap must be 0.07 to 0.18mm."
Worst-case
0.010 to 0.190 mm
FAIL, both limits violated
RSS (1σ)
0.041 to 0.159 mm
FAIL, minimum too tight
Recommended fix
Increase pin OD nominal to 19.870mm and tighten housing bore to ±0.020mm → gap becomes 0.075 to 0.185 mm, PASS
Free, no sign-in
Quick 1D stack-up calculator
For a linear dimension chain. Enter each nominal dimension and its ± tolerance.
Nominal (mm)
± Tolerance (mm)
Monte Carlo assumes:
Nominal stack
46.300 mm
Worst-case ±
±0.100 mm
RSS (99.73%) ±
±0.062 mm
Monte Carlo (99.73%)
-0.061 to 0.060 mm
Worst-case, RSS, and a 20,000-sample Monte Carlo simulation, all done client-side, nothing sent anywhere. With normal distributions, Monte Carlo converges to the same range as RSS, that's expected; switch to uniform to see how a conservative assumption changes the range. For violation flags, GD&T-aware chains, and dimensions pulled straight from a drawing, run it in the full workspace.
Full analysis, freeCapabilities
Full tolerance analysis in one tool
Worst-case, RSS & Monte Carlo
Run worst-case (WC), root sum square (RSS), and Monte Carlo tolerance stack-ups. See the gap range, assembly yield estimate, and which dimension chain is the controlling variable, with Monte Carlo for chains where a normal distribution isn't a safe assumption.
Upload CAD or paste dimensions
Upload STEP, DXF, or PDF drawings and ForgePilot extracts the dimension chains. Or paste your dimensions and tolerances directly into the prompt.
Automatic violation detection
ForgePilot flags any dimension chain where the stack-up closes out of spec under worst-case conditions, with the exact violating dimension highlighted.
Corrective tolerance recommendations
For each violation, get a specific tighter tolerance recommendation with the tradeoff cost: machining class, process change, or design revision.
GD&T-aware analysis
ForgePilot understands geometric tolerances (flatness, perpendicularity, true position) and includes them in the stack-up where specified.
Export analysis report
Export the full stack-up table and narrative as a PDF or Markdown report, ready to attach to a design review or supplier package.
Common stack-up scenarios
Any dimension chain with a critical gap or fit, ForgePilot handles it.
Shaft-hole fit analysis
H7/g6 and similar fits: interference, clearance, and transition check.
Assembly gap analysis
Multi-component stacks where gap closure is safety-critical.
PCB mounting tolerance
Connector, standoff, and board edge dimensional chains.
Weld joint geometry
Weld gap, joint prep angle, and root opening stack-up.
Optical system alignment
Lens centering, focal plane, and mounting tolerance chains.
Medical device assembly
ISO 13485 compliant tolerance analysis for implant and device fits.
Frequently asked questions
Is the tolerance stack-up calculator on this page free?
Yes. The calculator above runs entirely in your browser, no sign-in, no data sent anywhere, and it's free with no limit. It handles simple linear worst-case and RSS stack-ups. For GD&T-aware chains, dimensions pulled from a drawing, and automatic violation flagging, use the full workspace, also free to start.
What is a tolerance stack-up calculator?
A tolerance stack-up calculator analyzes a chain of dimensions and their tolerances to determine the cumulative variation at a critical gap or interface. It tells you whether your assembly will always close within spec (worst-case) and the statistical yield (RSS). ForgePilot does this from your dimension inputs or CAD files without requiring a spreadsheet.
What is the difference between worst-case, RSS, and Monte Carlo tolerance analysis?
Worst-case (WC) analysis assumes every dimension is at its worst allowable value simultaneously, guaranteeing 100% yield but often producing very tight tolerances. Root Sum Square (RSS) analysis treats variations statistically, assuming a normal distribution, and typically gives a more economical tolerance set at a defined yield level (e.g., 99.73% at plus or minus 3 sigma). Monte Carlo simulation samples each dimension thousands of times from its assumed distribution, normal or uniform, and reports the resulting range directly. For normally distributed dimensions, Monte Carlo converges to the same result as RSS; its real value is for chains where a normal distribution is not a safe assumption. ForgePilot calculates all three.
Can ForgePilot read dimensions from a drawing or CAD file?
Yes. Upload a PDF drawing, DXF, or STEP file and ForgePilot extracts the relevant dimension chains for the analysis. You can also describe or paste dimensions directly into the chat.
Does it support GD&T tolerances?
Yes. ForgePilot understands form, orientation, and position tolerances (flatness, perpendicularity, true position, etc.) and includes them in the stack-up when specified in your drawing or prompt.
Why does tolerance stack-up analysis matter?
Because it answers the expensive question before you commit to tooling: will these parts actually fit together in production. Poor tolerance management is a real, recurring source of assembly rework, catching a stack-up problem on paper costs an edit; catching it on the line costs scrapped parts and a delayed program.
Can I run a tolerance stack-up before parts are manufactured?
Yes, that is the point of the analysis. It works entirely from your dimensions and tolerances, on paper or in CAD, so you find out whether an assembly will close in spec before the first prototype exists, not after.
Related tools
Run your tolerance stack-up now
Upload a drawing or describe your dimension chain. Get worst-case, RSS, and Monte Carlo results, violations flagged, and fix recommendations in seconds.
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