Siding Calculator
Enter exterior wall area — get fiber cement siding board count. 10-15% waste recommended for eaves and windows.
Result
Enter material and area.
What this tool does
The siding calculator computes fiber-cement siding board count and total weight from exterior wall area and a waste factor. The reference spec is the Korean standard distribution size of 200×3600mm (0.72㎡/board, 9kg/board). A default waste of 10% covers cutting loss; increase to 15% when eave overhangs and window frames have not been deducted from the input area.
Who uses this
- Timber-frame house exterior siding replacement or new installation
- Pricing materials for rural or multi-unit residential exterior cladding
- Optimise order quantity after deducting openings for windows and doors
- Compare material quantities before requesting contractor quotes
- Plan delivery logistics given the 3.6m board length and weight
How to use (3 steps)
- 1Enter the exterior wall area (m²). If you have already subtracted window and door openings, use a lower waste factor; if you input gross wall area, use 15-20%.
- 2Set the waste factor (%). Default 10% applies when openings are already deducted. Use 15% for gross area input or lap-siding overlap.
- 3Click Calculate to get board count (rounded up) and total weight with step-by-step workings.
Formula & reference
Board spec: 200mm × 3600mm = 0.72㎡/board, 9 kg/board Adjusted area = installation area × (1 + waste% / 100) Board count = ceil(adjusted area ÷ 0.72) Total weight = boards × 9 kg Fiber-cement lap siding notes: - Typical lap overlap 30-50mm → exposed face ~150-170mm of 200mm width - Effective coverage per board ≈ 0.54-0.61㎡ when lapped - For lap installation, use waste factor 15%+ to account for overlap loss - Corner trim and J-channel material calculated separately Recommended waste: straight wall (openings deducted) 10% / gross area input 15% / complex shapes 20%
Real examples
Example 1: Single-storey house exterior (80㎡ net wall, 10% waste)
Adjusted area = 80 × 1.10 = 88㎡. Boards = ceil(88 ÷ 0.72) = 123 boards. Weight = 123 × 9 = 1,107kg. Plan one truck delivery.
Example 2: Lap installation with 30mm overlap (60㎡, 15% waste)
Effective coverage with overlap = ~0.612㎡/board. Adjusted area = 69㎡. Boards = ceil(69 ÷ 0.72) = 96 boards. 15% waste absorbs overlap and cutting loss.
Example 3: Multi-unit residential (200㎡ gross wall, 40㎡ openings)
Net wall = 160㎡. 10% waste → adjusted 176㎡. Boards = ceil(176 ÷ 0.72) = 245 boards. Weight 2,205kg — confirm heavy-lift equipment availability.
Frequently asked questions
What is the difference between fiber-cement and vinyl siding?
Fiber-cement (cement, sand, and cellulose fibre) is fire-resistant, durable, and can replicate a wood-grain finish. Vinyl (PVC) is lighter and cheaper but can deform in heat and fade over time. This calculator uses the fiber-cement spec.
Does lap installation require more boards than vertical?
Yes. Horizontal lap siding overlaps 30-50mm per course, reducing effective coverage per board to about 0.60-0.66㎡ versus the nominal 0.72㎡. Expect to order 10-15% more boards than a straight-coverage calculation would suggest.
Are corner trim and J-channel included?
No. This calculator covers siding board count only. Corner trim, J-channel, starter strip, and window flashing must be calculated separately.
When should I use 10% vs 15% waste?
Use 10% if you have already subtracted opening areas from your input. Use 15-20% if you are entering gross wall area (openings not deducted), or if you are accounting for lap-siding overlap.
Why does weight matter for siding?
Fiber-cement at 9kg/board is more than twice the weight of vinyl (4kg). At 100+ boards you exceed half a tonne, which affects vehicle selection and site handling. For upper-storey work, scaffold loading also needs checking.
How do I measure exterior wall area?
Measure each wall face as width × height, then sum. Decide whether to subtract window and door areas — if not, raise the waste factor. For gable-end walls, treat the triangular section as average height × width.
Cautions
- •Based on 200×3600mm fiber-cement siding spec. Other siding types or sizes need separate calculations.
- •Lap installation reduces effective board coverage — adjust waste factor upward to 15% or more.
- •Corner trim, J-channel, starter strip, and flashing are not included in this calculation.
- •Board weight is substantial; confirm vehicle capacity and site handling equipment before ordering.
- •House wrap (weather-resistant barrier) behind the siding is a separate material not covered here.
Last reviewed: 2026-06-17