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Default Calculation Assumptions

These are the baseline values baked into each calculator before you change them. They are starting points, not quotes.

Waste allowances

| Job type | Default | When to increase | |----------|---------|------------------| | Concrete pour | 10% | Irregular forms, steep access | | Flooring / tile | 10% | Diagonal lay, many alcoves | | Decking boards | 10% | Lots of posts, stairs | | Mulch | None (depth is net) | Add extra if topping deep beds | | Roofing | 10% | Hips, valleys, dormers |

Openings (paint)

  • Door: 21 ft² (US) / 1.95 m² (UK) deducted per door
  • Window: 15 ft² (US) / 1.4 m² (UK) per window

Large picture windows or double doors — reduce the count or lower the deduction manually.

Sheet and roll sizes

  • Drywall: 4×8 ft (32 ft²) or 1200×2400 mm
  • Insulation batt roll: ~40 ft² or ~5.8 m² per roll (change to match your pack)

Fence defaults

Panel width and post spacing default to 8 ft (2.4 m). Panel systems vary — enter what your kit specifies.

Cost estimator

  • Materials waste: 10% unless you change it
  • Markup: 0% for homeowners; trades may add 10–20% on quotes
  • Output range: ±10% on the total

Your job may differ

Local code, product labels, and site conditions always win over a website default. Use these tables to see what we assumed — then adjust the inputs.