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CALCULATORS / ASSEMBLY, CAPACITY AND MANUFACTURING ECONOMICS

BOM and assembly unit-cost estimate calculator

Two line-item BOM with supplied scrap allowance; account units.

manufacturing-bom-cost.napkin / editable
✓ checks pass

SCENARIO COMPARISON

Compare the numbers.

This source describes an analytical model. Its quantities and checks are the view.

ScenarionetCostpurchaseCost
1818.9474
16.417.2632

All calculated quantities are listed with the inputs. Switch to Source to inspect the equations.

SCENARIOS / CALCULATED VALUESSAME SOURCE

Change an input to see the consequences.

unit BOM budget18.95 ✓ passes

BASELINE INPUTS

CALCULATED

netCost18
purchaseCost18.947

Edits change the baseline source.

Calculated from your source · not saved
Baseline · Baseline
unit BOM budget18.95 ✓ passes
alternative · alternative
unit BOM budget17.26 ✓ passes

Illustrative first-order example. Checks are editable requirements, not design standards. The broader topic may require additional equations, data, and validation.

Formula and units

This example uses the following equations. Input names and units match the editable source above.

net cost
netCost = quantityA*costA+quantityB*costB
purchase cost
purchaseCost = netCost/(1-scrapFraction)

Original worked example

These are the baseline values in the downloadable source. Edits above let you test your own values.

Given

quantity a
4
cost a
2
quantity b
2
cost b
5
scrap fraction
0.05

Calculated

net cost
18
purchase cost
18.9474

Assumptions and limits

Two line-item BOM with supplied scrap allowance; account units.

The requirement checks use the limits written in this example. Passing a check does not establish that the model covers every load, material behavior, or operating condition in a real design.

Download this .napkin example ↓

Take it further with your agent

Napkin keeps the inputs, equations, checks and assumptions together in one study. Your agent sets it up; you change the numbers.

Try with Claude ↗

codex 'Use Napkin (https://napkin.engineering/mcp, or the local Napkin plugin) to build a study: BOM and assembly unit-cost estimate. Inputs: quantities; part prices; assembly labor; scrap. Outputs: unit and batch cost; cost drivers. Model scope: Explicit process times, yield and costs supplied by the user. Read napkin_capabilities and the current snapshot. Ask me for the values that matter, label assumptions with units, author .napkin source, validate it and apply it with napkin_source using the current revision, then open the study. Add checks for the limits I supply. Keep unsupported analyses explicit.'

Claude needs the Napkin connector; Codex needs the Napkin plugin. Set up your agent ↗

The broader study

The topic brief below describes the broader scope. The worked example above states the particular calculation it implements.

  • Inputs: quantities, part prices, assembly labor, scrap
  • Outputs: unit and batch cost, cost drivers
  • Modes: calculate, compare, sweep
  • Drawing: Process graph and cost curves

EXECUTABLE WORKED EXAMPLE · FIRST-ORDER MODEL · CHECK THE SCOPE & ASSUMPTIONS

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