Window Estimation Formula — The Professional Calculation

The formula professional window estimators use. Every variable explained — from profile metreage to labour hours to target margin. Build your estimate on fundamentals, not guesswork.

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The Window Estimation Formula in Detail

Four calculations combine to produce an accurate estimate. Every professional uses these — Doorwin automates them.

1

Profile Metreage × Cost per Metre

Frame perimeter + all mullions + all transoms = total linear metres of profile. Multiply by your per-metre cost for the chosen profile system. Include a 5-8% waste factor — cutting optimisation is never 100% efficient in real workshops.

2

Glass Area × Cost per m²

For each glazed panel: clear opening width × clear opening height = glass area. Sum across panels. Multiply by glass specification cost per m² (DGU, TGU, laminated, etc.). Add edge-seal perimeter cost for warm-edge spacer specifications.

3

Fixed Hardware × Quantity

Per window: count locks, hinges, handles, trickle vents, striker plates, friction stays. Multiply by unit cost. Hardware varies heavily by spec — a budget 2-lock 2-hinge casement runs £15-25; a tilt-turn with multi-point locking runs £80-130. Not an afterthought — a defining cost block.

4

Labour Hours × Rate + Overhead + Margin

Fabrication hours (typically 1.5-3 hrs per window) × shop rate + install hours (typically 1-2 hrs per window for 1st floor) × fit rate + overhead allocation (usually 12-18% of direct cost) + target margin (15-25% for residential, 8-15% for commercial volume). That's your sell price.

Frequently Asked Questions

What's the simplest version of the window estimation formula?
Sell price = (material cost × 1.6-1.8) for trade supply-only, or (material cost × 2.2-2.8) for retail supply-and-install. These multipliers implicitly cover labour, overhead, and margin. Useful for quick sanity-checking — but shouldn't replace line-by-line estimation on any real job.
How many labour hours should I allocate per window?
Fabrication: 1.5 hrs for standard casement, 2 hrs for tilt-turn, 2.5-3 hrs for bay/bow window, 4+ hrs for arched or shaped specials. Install: 1 hr for ground floor standard, 1.5 hrs for first floor, 2+ hrs for scaffold access. Adjust for your workshop's actual throughput by measuring against 10-15 completed jobs.
What overhead percentage should I apply?
Typical small-to-medium fabrication/install business: 12-15% of direct cost. Includes: workshop rent, utilities, non-productive labour (office, management), insurance, vehicles, tooling depreciation, marketing. Businesses with retail showrooms or heavy sales overhead run 18-22%. Know yours — undercosting overhead is the #1 cause of unprofitable projects.
Does Doorwin use this formula or something else?
Exactly this formula. Every component is exposed and configurable — per-metre profile cost per system, per-m² glass cost per spec, hardware cost per item, hour rates per role, overhead percentage, margin percentage. Your inputs, the correct formula, automatic output. Fast to set up and accurate from the first quote.

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Estimate With a Formula, Not a Gut Feeling

The formula is public. The accuracy comes from executing it consistently. Doorwin does that for you.

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