Inputs
Formula used
This calculator converts your inputs into an estimated count using an effective-coverage approach. Start with a base coverage, apply adjustment factors, then divide area by coverage and round up.
- BaseCoverage = CoverageArea (area method) or (Angle/360) × π × Radius² (radius+angle method)
- EffectiveCoverage = BaseCoverage × HeightFactor × PartitionFactor × EnvironmentFactor × (1 − Overlap%)
- SensorsPerZone = ceil(ZoneArea / EffectiveCoverage), then apply MinPerZone
- TotalSensors = ceil(BaseTotal × (1 + Margin%)) + EntranceAdd
How to use this calculator
- Enter total area and how many zones/rooms you are covering.
- Choose a coverage method: area per sensor, or radius plus angle.
- Set overlap and safety margin to match your design practice.
- Select obstruction level and environment for a realistic estimate.
- Click Calculate; review the breakdown and spacing estimate.
- Export CSV or PDF to attach to your layout notes.
Example data table
| # | Total area | Zones | Method | Base coverage | Overlap | Margin | Recommended sensors |
|---|---|---|---|---|---|---|---|
| 1 | 600 m² | 6 | Area | 80 m²/sensor | 15% | 10% | 10 |
| 2 | 15,000 ft² | 10 | Radius + angle | 18 ft @ 110° | 20% | 10% | 18 |
| 3 | 1,200 m² | 4 | Area | 120 m²/sensor | 10% | 15% | 14 |
Examples are illustrative; always confirm with product coverage charts and site conditions.
Practical notes
- For corridors, focus on line-of-travel detection patterns.
- In warehouses, racking can block sensors and cause blind spots.
- Outdoor sensors may require tighter spacing to limit false triggers.
- Use extra sensors at stairs, turns, and critical access points.
Coverage assumptions and typical ranges
Indoor motion devices often use 90–120° lenses and 10–20 m reach, translating to roughly 60–120 m² (650–1,300 ft²) of usable coverage after practical losses. On active sites, temporary partitions, stacked materials, and moving equipment reduce line‑of‑sight, so start near the lower end unless you have model‑specific coverage charts.
Using radius and angle for sector layouts
When radius and viewing angle are known, coverage is treated as a circular sector: (Angle/360) × π × Radius². For example, 18 m at 110° yields ~311 m² of base sector area before adjustments. This is useful for wall‑mounted devices and corridor “fan” patterns, then add overlap where adjacent zones must hand off without gaps.
Partition and environment adjustment factors
Two realism multipliers are applied: partition factor (open 1.00, moderate 0.85, high 0.70) and environment factor (indoor 1.00, semi‑outdoor 0.90, outdoor 0.85). A base 80 m² sensor in a moderate, semi‑outdoor area becomes 80 × 0.85 × 0.90 = 61.2 m² before overlap and height effects, helping quantify clutter and exposure.
Overlap and margin planning for reliability
Overlap allowance reduces net coverage to prevent blind spots near corners, columns, and stairwells. Many teams use 10–25% overlap on work floors, increasing it on high‑traffic routes. Safety margin adds spare devices for layout changes and commissioning; 5–15% is common. A base total of 12 sensors with a 10% margin often rounds to 14, before entrance add‑ons.
Interpreting results for procurement and placement
Treat “sensors per zone” as a starting grid, then refine with spacing (≈ √EffectiveCoverage). If effective coverage is 64 m², spacing is ~8 m on a square layout. Validate mounting height against typical ranges (about 2.2–3.5 m for many indoor units); mounting too high can reduce effective coverage and increase counts. Use the final total for purchasing, cabling, and test walk‑throughs. Document assumptions; update after site changes.
FAQs
Which coverage method should I use?
Use Area per sensor when the product datasheet provides a realistic m²/ft² figure. Use Radius + angle for sector-style patterns (typical wall mounts). Always validate the base number with the manufacturer’s layout diagram.
What overlap setting is reasonable?
For interior rooms, 10–20% overlap usually avoids gaps at corners and walk paths. For cluttered or outdoor areas, 20–30% is safer. Higher overlap increases sensor count because effective coverage shrinks.
Does this estimate meet regulatory requirements?
It is a planning estimate, not a compliance certificate. Final placement should follow the project specification, local codes, and the sensor manufacturer’s coverage charts. Use a site walk-through to confirm detection performance.
How do partitions change the result?
Partitions reduce effective coverage using factors: open 1.00, moderate 0.85, high 0.70. Choose “high” for racking, stacked materials, or multiple obstructions. This increases sensors per zone to compensate for blocked line-of-sight.
Why does mounting height affect coverage?
Most devices are optimized for a typical mounting height. If you mount outside the common range, detection geometry and sensitivity can drop, reducing usable coverage. The calculator applies a small penalty to reflect that risk.
How should I model irregular areas or corridors?
Split the floor into more zones so each zone is more uniform. Increase overlap for turns and intersections, and use a minimum sensors-per-zone value. Add entrance sensors when doors or access points need dedicated coverage.