Free Roofing Calculator: How Many Iron Sheets Do You Need?
Free Roofing Calculator: How Many Iron Sheets Do You Need?
Free Roofing Calculator: How Many Iron Sheets Do You Need? is One of the most common questions we get at Builder Choice Mabati is: “Ninahitaji mabati ngapi?” – How many sheets do I need?
And it’s a fair question. Buy too few and you’re making costly top-up orders. Buy too many and you’ve locked up shillings in sheets sitting idle on site. Getting the number right from the start saves you money, time, and a lot of fundi frustration.
This guide walks you through exactly how to calculate the number of mabati sheets you need – step by step, with real examples – plus a quick-reference table for the most common Kenyan house sizes.
What you need before you start
You need three basic measurements from your roof:
- Roof length – the total horizontal length of each roof section (in metres)
- Roof slope length (rafter length) – the slanted distance from ridge to eave, not the wall height (in metres)
- Number of roof sections – a simple gable roof has 2, a hipped roof has 4, an L-shaped house may have 6+
Important: Always measure the slope length, not the wall height. The slope is always longer than the wall – this is where most people under calculate and run short.
Step-by-step: how to calculate your mabati
Area = Roof Length × Slope Length
Example: Your roof is 12 metres long and the slope is 4 metres from ridge to eave.
Step 1 – Calculate the area of one roof section
Area of one side = 12m × 4m = 48 square metres
Step 2 – Multiply by the number of sections
If it’s a simple gable roof (2 sides): 48m² × 2 = 96m² total roof area
Step 3 – Add your overlap allowance (10–15%)
Mabati sheets overlap slightly at the sides and ends to create a watertight seal. This means your actual sheet coverage is less than the raw area. Always add 10–15% to your total:
96m² × 1.12 (12% allowance) = 107.5m²
Step 4 – Divide by coverage per metre of sheet
Builder Choice Mabati sheets are sold per metre of length and have a standard effective cover width of approximately 0.86m (Box Profile) or 0.76m (Corrugated) after overlap.
For Box Profile: 107.5m² ÷ 0.86m = 125 linear metres of sheet needed
Since Builder Choice Mabati Factory cuts to your exact length – say you need 4-metre sheets – that’s 125m ÷ 4m = 32 sheets (round up to 33 for safety).
Builder Choice Mabati cuts sheets to your exact specified length. This means zero offcuts, zero waste – and you only pay for exactly what goes on your roof.
Quick reference – common Kenyan house sizes
| House Type | Approx. Roof Area | Linear Metres Needed | Estimated Cost (G30 Box Matte) |
| 2-bedroom (simple gable) | 80–100 m² | 95–120 lm | KSh 54,150–68,400 |
| 3-bedroom (gable) | 120–160 m² | 140–190 lm | KSh 79,800–108,300 |
| 3-bedroom (hipped) | 150–200 m² | 175–235 lm | KSh 99,750–133,950 |
| 4-bedroom (hipped) | 200–280 m² | 235–330 lm | KSh 133,950–188,100 |
| Commercial/warehouse | Varies | Get a free quote | Call 0722 818 240 |
Estimates based on KSh 570/m for G30 Box Profile Matte. Prices subject to confirmation.
Don’t forget the accessories
The sheets are the main cost – but your roof isn’t complete without these:
- Ridge Cap – KSh 570/m (G30). Runs along the peak of the roof. For a standard 3-bedroom, budget 10–15 metres.
- Roof Valley – KSh 570/m (G30). Needed wherever two roof sections meet at an angle. Count your valleys.
- Barge Boards – KSh 570/m (G30). Finish the edges at the gable ends.
- Builder Roll Top – KSh 570/m (G30). Seals the top edge where the sheet meets the ridge.
- Roofing Nails – KSh 240/kg. Rough rule: 1kg per 15–20 square metres of roof.
- Rubber Washers – KSh 140/pack. Non-negotiable – every nail needs one to prevent leaks.
One rubber washer per roofing nail. This is not optional. A nail driven without a rubber washer is a future leak waiting to happen – guaranteed.
Real example – 3-bedroom house in Nairobi
Let’s say you’re building a 3-bedroom house in Ruaka with a standard hipped roof. Your fundi gives you these measurements:
- Roof length: 14m × 8m footprint
- Slope length: 3.5m per side
- 4 roof sections (hipped)
Calculation:
- Area per section: 14m × 3.5m = 49m² (×2 long sides) + 8m × 3.5m = 28m² (×2 short sides)
- Total area: 98m² + 56m² = 154m²
- With 12% overlap: 154 × 1.12 = 172.5m²
- Linear metres (Box Profile, 0.86m cover): 172.5 ÷ 0.86 = 201 linear metres
- Cut at 3.5m lengths: 201 ÷ 3.5 = 58 sheets (round to 60)
Estimated cost at KSh 570/m (G30 Box Profile Matte):
201m × KSh 570 = KSh 114,570 for the main sheets alone.
Add ridge cap (14m × KSh 570 = KSh 7,980), roof valley, nails, and washers – and your full roofing materials budget for this house sits around KSh 130,000–145,000, excluding fundi labour.
The easiest way – just call us
Don’t want to do the maths yourself? You don’t have to. Share your house plans or measurements with the Builder Choice Mabati team and we’ll give you a free, accurate quote – specifying exact sheet lengths, quantities, and accessories.
We’ve helped hundreds of Kenyan homeowners get their roofing materials exactly right, with no overpaying and no running back for top-ups.
Get your free roofing quote today
Call / WhatsApp: 0722 818 240
builderchoicemabati.co.ke | Kasarani-Mwiki Road, Nairobi
Factory-direct pricing. Cut to your exact length. Free delivery countrywide.