Inputs
Example data table
| Room | Shape | Inputs (m) | Area (m2) |
|---|---|---|---|
| Living Room | Rectangle | 5.5 × 4.2 | 23.10 |
| Bedroom | Rectangle | 4.0 × 3.6 | 14.40 |
| Kitchen | Rectangle | 3.6 × 3.0 | 10.80 |
| Lobby (irregular) | Custom | Surveyed 7.5 | 7.50 |
| Rooms subtotal | 55.80 | ||
Formula used
- Rectangle room:
Area = Length × Width - L-shape room:
Area = (L1×W1) + (L2×W2) - Circle room:
Area = pi × r^2 - Net usable per floor:
Net = Sum(Room Areas) − Stair/Void − Shaft - Gross per floor:
Gross = Net + Net×Circulation% + (Net+Circulation)×Wall% + Add-ons - Total built-up:
Total = (Gross + Extra per floor)×Floors + One-time add-ons
How to use this calculator
- Select your unit system and enter the number of floors.
- Add rooms and choose a shape for each room.
- Enter dimensions or a custom area for irregular rooms.
- Enter deductions for stairs, voids, or service shafts if needed.
- Optionally add balconies, garages, and porches, then choose whether they count once or per floor.
- Press Calculate to see results above the form.
- Use the download buttons to export CSV or PDF reports.
Why net and gross area differ
Net usable area reflects spaces you can occupy and furnish, based on the sum of room areas minus defined voids. Gross floor area expands that figure by adding circulation and wall allowances, plus optional attached elements. Reporting both values helps align design intent, budget control, and permitting documentation.
Room-by-room takeoff workflow
Start with a consistent room list per typical floor and capture dimensions from drawings or site measurements. Use rectangles for most rooms, L-shapes for stepped layouts, and custom entries for surveyed irregular spaces. Keep names stable across revisions so changes in area can be tracked and reviewed.
Allowances and deductions you should document
Circulation allowance represents corridors, landings, and movement zones that are not always drawn as rooms. Wall allowance accounts for construction thickness and structural zones that reduce usable space. Deductions for stair voids and service shafts should be supported by plan callouts to avoid double counting.
Multi-floor aggregation and add-ons
Typical-floor calculations scale quickly for multi-storey houses by multiplying gross area by the number of floors. Add-ons such as balconies, porches, and garages can be counted once or repeated per floor, depending on design. Extra area per floor is useful for shared cores, mechanical rooms, or thickened perimeter zones.
Using exported reports in estimating and approvals
Exported CSV and PDF outputs provide a clean audit trail for consultants, clients, and review authorities. Share net area for occupancy planning and furnishing layouts, and use gross area for cost and compliance checks. Maintain the same input assumptions across alternatives to compare designs fairly.
- Rooms subtotal: 55.80 m2, Stair void: 3.50 m2, Shaft: 0.80 m2.
- Circulation: 8%, Walls: 6%, Floors: 2.
- One-time add-ons: Balcony 6 m2, Garage 18 m2, Porch 4 m2.
- Typical outcome: Net ≈ 51.50 m2/floor, Gross ≈ 59.60 m2/floor, Total built-up ≈ 147.20 m2.
FAQs
1) What is the difference between net and gross area?
Net is usable room space after deductions. Gross adds circulation and wall allowances, plus selected add-ons, giving a value closer to built-up area.
2) Should balconies and garages be counted once or per floor?
Count them once when they exist only at ground level or as a single attached element. Count per floor when a repeated feature occurs on each level.
3) How do I handle irregular rooms?
Use the Custom area option when you have a surveyed value, or break the shape into rectangles or an L-shape so the calculation matches the drawing takeoff.
4) What circulation percentage should I use?
Use a value consistent with your project type and local practice. Smaller layouts may use lower values, while complex plans with long corridors often require higher allowances.
5) Why subtract stair voids and shafts?
Open-to-below areas and service shafts reduce usable floor space. Deducting them helps prevent overstating occupancy area and improves consistency when comparing design options.
6) Can I calculate a single floor only?
Yes. Set floors to 1 and enter rooms for that level. You can still use add-ons and deductions to match the floor plan and export the results.
7) Why export CSV and PDF?
CSV supports further estimating and tracking in spreadsheets, while PDF is convenient for sharing a fixed snapshot with stakeholders, reviewers, and project records.