Picture yourself standing on your plot, building permit in hand, with one question on your mind: how many blocks do I need? How much cement, steel, tile, paint? This guide is written for you specifically — someone with no engineering background who doesn't want complicated jargon. We'll go step by step, with worked examples, so you leave able to build your own bill of quantities, know exactly what to buy, and spot it if anyone tries to inflate your invoice.
Before we start — a golden rule: all the figures here are approximate, meant to give you a realistic picture and protect you from inflated invoices. The final approved quantities for execution must come from the engineering office that designed your plans, because steel and concrete quantities in particular depend on the structural design and the safety of the building. Use this guide to understand and review, not to build blindly.
1. Where to start: the key number in your permit
Before calculating any material, you need one core number: the total built-up area (the sum of all floor areas in square meters). You'll find it in your building permit and approved plans.
Key terms in the permit:
- Building ratio (coverage): the percentage of the plot you may build on per floor. Example: a 400 m² plot with a 60% ratio means you build 240 m² per floor.
- Number of permitted floors: e.g. ground + first + roof annex.
- Total built-up area: floor area × number of floors. This is your base number for everything.
An example we'll use throughout: a villa on a 400 m² plot, building 240 m² per floor, two floors (ground + first). Total built-up area = 240 × 2 = 480 m². We return to this number at every step.
2. Building stages = calculation stages
Any building splits into two stages, each with its own materials:
- Structure (the skeleton): excavation, foundations, columns, tie beams, slabs, and block walls. Materials: concrete + steel + blocks + cement.
- Finishing: plastering, tiling/ceramic, painting, electrical, plumbing. Materials: plaster cement + tiles + paint + wiring + pipes.
3. Calculating blocks
The standard Saudi block is 20×20×40 cm. Its visible face in the wall = 40 cm × 20 cm = 0.08 m².
The method, simply:
- Calculate wall area = (length × height) for each wall, then add them up.
- Subtract door and window openings.
- Each square meter of wall needs about 12–13 blocks.
- Add 5% waste (breakage and cutting).
Example: a villa with 600 m² of total wall area (after subtracting openings). Blocks = 600 × 12.5 = 7,500, + 5% waste = 7,875 (round to 7,900).
Cement for laying blocks
The mortar binding the blocks needs cement. The practical rule used in Saudi Arabia: one 50 kg cement bag lays about 120–140 blocks.
Example: 7,900 blocks ÷ 130 = about 61 cement bags for laying blocks alone.
4. Calculating concrete and cement
Concrete = cement + sand + gravel + water, always measured in cubic meters (m³), i.e. (length × width × thickness).
Concrete for slabs
Simple rule: concrete volume = slab area × thickness. A typical solid slab is about 15 cm (0.15 m) thick.
Example: a 240 m² slab at 0.15 m → slab volume = 36 m³. Adding beams and columns (× 1.4 roughly) → about 50 m³ per floor including all elements.
Cement inside the concrete
One cubic meter of reinforced concrete needs roughly:
- 7 cement bags (50 kg) — about 300–350 kg of cement per m³.
- 0.8 m³ gravel approximately.
- 0.4–0.5 m³ sand approximately.
Example: a 50 m³ slab → cement = 50 × 7 = 350 bags | gravel ≈ 40 m³ | sand ≈ 25 m³.
The easier path: you'll usually buy ready-mix concrete from the plant by the cubic meter, so you won't calculate cement, sand and gravel yourself — just order the cubic meters + 2–3% waste. Manual calculation matters only if you mix on site.
5. Calculating reinforcement steel
Steel is the backbone of the building, and its quantity depends on the structural element. General rule: each cubic meter of concrete needs 80 to 120 kg of steel (average 100 kg). By element:
| Structural element | Steel per m³ of concrete |
|---|---|
| Foundations | ≈ 45 kg |
| Tie beams | ≈ 40 kg |
| Columns | ≈ 120 kg |
| Slabs | ≈ 80–100 kg |
Quick rule for slabs: every 100 m² of slab needs roughly 1.2 to 1.5 tons of steel and 15 m³ of concrete (at 15 cm thickness).
Example: total concrete for the villa ≈ 110 m³. Approximate steel = 110 × 100 kg = 11,000 kg = 11 tons, + 5% waste (laps and offcuts) = about 11.5 tons.
6. Calculating plaster
Plaster is the cement layer covering walls before painting, measured per square meter per face. Rule: one 50 kg cement bag plasters about 10 m² (at ~2 cm thickness).
Example: plaster area (interior + exterior) = 1,100 m² → cement = 1,100 ÷ 10 = 110 bags, plus sand at about 1:4.
7. Calculating tiles and ceramic
The easiest method is to calculate by square meter, not by piece (you buy by the meter):
- Floors: area = length × width per room, summed.
- Walls (bathrooms and kitchens): area = room perimeter × tiling height. (Perimeter = (length + width) × 2.)
- Add everything up and add waste.
Bathroom example: 2 × 2.5 m, walls tiled to 2.8 m height. Floor = 5 m². Walls = (2 + 2.5) × 2 × 2.8 = 25.2 m². Total = 30.2 m² (subtract door and window ≈ 2 m² → 28 m²), + 10% waste = about 31 m² of tile.
Cement for fixing tiles: one 50 kg cement bag fixes about 7 m² of ceramic (or use ready adhesive for large porcelain, calculated per the package instructions).
8. Calculating paint
Paint is calculated as area × number of coats ÷ coverage rate. Rule: each 1 kg/liter of paint covers about 10 m² per coat. A wall typically needs 3 coats: a primer/putty coat + two paint coats.
Example: wall area to paint = 1,000 m², two coats → quantity = (1,000 × 2) ÷ 10 = 200 kg of paint (about 11 cans of 18 liters), + 5–10% waste → about 215 kg.
9. Calculating electrical and plumbing (where people get overcharged most!)
Electrical and plumbing are calculated differently — not by square meter, but by counting points. A point = any outlet: a light, switch, socket, AC unit, tap, toilet, etc.
Electrical
- Count electrical points from the plan (lighting + sockets + AC).
- Each point uses about 15–20 meters of wire (depending on distance from the distribution board).
- Rule of thumb: an average villa (480 m²) has about 150–200 electrical points.
- Add 10–15% waste for wiring.
Example: 180 points × 17 m average = 3,060 m of wire → + 12% waste ≈ 3,430 m (spread across 1.5 / 2.5 / 4 mm sizes by load).
Plumbing
- Count water points (hot + cold) and drainage points per bathroom and kitchen.
- Water pipes are usually PEX or PPR; drainage pipes are PVC.
- Estimate the line length from the source to each point, or use ≈ 8–12 m of pipe per full bathroom.
- Add 10% waste + fittings (elbows, tees) at about 15% of the pipe count.
Important note: electrical and plumbing are among the hardest items for a non-specialist to estimate precisely because they depend entirely on the plan. Get the quantity sheet (points + lengths) from your engineering office or contractor in writing, and compare it to these rules — if you find a big gap, ask why.
10. Waste factor table — keep it
Waste is the extra quantity you buy above the calculated amount, to cover breakage, cutting and fittings. Don't add too much (wasted money) or too little (work stoppage).
| Material | Waste / extra | Reason |
|---|---|---|
| Blocks | 5% | Breakage in transport and laying |
| Ready-mix concrete | 2–3% | Minor spillage and loss |
| Reinforcement steel | 3–5% | Laps and offcuts |
| Cement | 5% | Dust loss and hardened bags |
| Ceramic / standard tile | 5% | Corner cutting |
| Diagonal or large-format tile | 10% | More cutting and breakage |
| Marble / large porcelain | 10–15% | Fragility and precise cutting |
| Paint | 5–10% | Surface absorption and first coat |
| Electrical wiring | 10–15% | Loops, runs and outlets |
| Plumbing pipes | 10% | Cutting and fittings |
11. How to split your budget? (approximate cost shares)
To tell whether an item is overpriced, here are approximate shares of total build cost:
| Item | Share of cost |
|---|---|
| Structure (skeleton) | 11–13% |
| Concrete | 6–8% |
| Steel | 7–9% |
| Plumbing works | 10–12% |
| Air conditioning | 11–13% |
| Tiling and ceramic | 8–10% |
| Painting | 7–10% |
Quick summary to pin on the wall
| Material | Golden rule |
|---|---|
| Blocks | 12–13 blocks / m² of wall + 5% |
| Cement for blocks | 1 bag / 120–140 blocks |
| Concrete | area × thickness (m³) |
| Cement in concrete | 7 bags / m³ |
| Steel | 80–120 kg / m³ (or 1.2–1.5 tons / 100 m² slab) |
| Plaster | 1 cement bag / 10 m² |
| Ceramic | area ÷ tile area + 5–10% |
| Paint | kg / 10 m² per coat × number of coats |
| Electrical | points × 15–20 m wire + 12% |
| Plumbing | count points + 10% waste |
Conclusion
Calculating a bill of quantities is not hard science nor exclusive to engineers — it's simple logic: know your areas, apply the rule, add the waste. Once these numbers are in your hands, you move from someone who "buys on the contractor's word" to someone who reviews, compares and decides — and that alone saves you thousands and protects you from inflated invoices.
Remember: use this guide to understand and review, and always rely on the final quantities from your engineering office before execution — especially for steel and concrete, which are a matter of safety before cost.
Share this guide with anyone planning to build — knowledge is a shield, and a house built with understanding comes out stronger and cheaper. We wish you a successful build and a home that gathers your loved ones in good health.
