BOM Costing for Furniture: Waste, Cost per Product and Margin
Build a bill of materials that survives contact with the workshop: waste allowances per material class, honest roll-ups, and margin maths that does not underprice.
The BOM is a purchasing document
A bill of materials lists what one product consumes, but a workshop buys materials, not consumption: the 0.030 m³ of acacia in a table leg means purchasing 0.0375 m³ once a realistic 25% rough-lumber waste is applied. Industry planning figures put dried S4S lumber waste at 15-20%, rough-sawn at 25-30% (poor stock reaches 40-50%), nested panels at 5-12% against roughly 15% for manual cutting, and hardware at 1-5%. BOM cost carries those presets on every waste field, editable per line.
Worked example: one acacia side table
Four legs at 0.030 m³ each of acacia at $750/m³ with 25% waste cost $112.50. An MDF top needing 3.2 m² from 2.98 m² sheets at $22 with 12% waste takes 1.2 sheets, $26.46. A hardware set at $8.50 with 3% waste rounds to $8.76. Total material cost: $147.72 for the batch. This is the arithmetic BOM cost automates - net quantity, waste multiplier, unit cost, one line each.
Rolling up to cost per product
Material cost divided by the number of products in the batch, plus direct labour per product, is the floor price. What the floor excludes matters as much: finishing consumables, glue (its own calculator lives at Wood glue), machine tooling, electricity, rent and freight all sit above it. The cost-per-product figure is where batch size shows its leverage - spreading one setup across fifty tables instead of five moves the labour component without touching the BOM.
Margin: the difference between price and hopeful pricing
Margin is taken on the selling price, so the sell price is cost / (1 − margin). A $63.34 product at a 30% margin quotes at $90.49; adding 30% to cost and calling it $82.34 leaves you advertising a margin you are not earning. The confusion is so common that pricing software builds in a warning. BOM cost applies the margin formula directly and shows the profit per product next to the price it implies.
Keeping the BOM alive
A BOM is a model of the workshop, and workshops drift: lumber prices move, waste improves after a nesting-software investment, hardware substitutes appear. Re-cost flagship products quarterly, measure actual waste against the preset occasionally, and let the yield chain at Manufacturing yield reconcile the roundwood purchase with the products that actually shipped. The workshops that survive squeezes are the ones whose costing was already honest when the squeeze arrived.