By Intellect Architects | Updated October 2025
Every solid building starts from the ground — literally. Foundation blinding might look like “just a small layer of concrete,” but any site engineer who’s ever dealt with messy trenches knows how much difference it makes. Let’s break down how to calculate the number for your blinding, in clean metric units — just as we do on site in Ebonyi, or for some other states in Nigeria.
Keynotes
- Understand what blinding does beneath your footing.
- Learn how to calculate its volume using simple site math.
- Estimate materials accurately — no waste, no guesswork.
This is the kind of math every site supervisor should master before the mixer starts rolling.
What Exactly Is Foundation Blinding?
Blinding is that thin, plain-concrete layer — usually 50 mm to 100 mm thick — poured at the base of your foundation trenches. It’s not reinforced; it’s just there to create a clean, level bed before placing the main footing. Think of it as the *make-up layer* that keeps your structural concrete from touching raw soil.
Why It Matters More Than People Think
On paper, blinding seems minor. But on site, it’s what saves your footing from uneven ground and contamination. Here’s why it’s worth doing right:
- Keeps soil out: Prevents loose earth from mixing into your footing concrete.
- Gives you a flat base: Perfect for setting rebar and formwork accurately.
- Reduces waste: No need to “top up” uneven trenches with extra mix.
- Improves durability: Creates a stable, bonded base for the main structure.
Ask anyone who has poured on bare soil — you’ll never skip blinding twice.
Step-by-Step: How to Calculate the Volume
Now, the math. Don’t worry — you won’t need AutoCAD or LibreCAD for this.
1. Measure the Total Length of the Trench
Walk it. Literally. Measure around the full perimeter where you’ll pour. Let’s say it’s 80 m.
2. Measure the Average Width
Residential trenches are usually between 600 mm and 900 mm. We’ll use 0.7 m as average width.
3. Check the Thickness of Blinding
Depending on your soil and design, it’s normally between 0.05 m and 0.1 m. Let’s go with 0.075 m.
4. Multiply to Get the Volume
Volume = Length × Width × Thickness
Volume = 80 × 0.7 × 0.075 = 4.2 m³So you’ll need roughly 4.2 cubic meters of concrete for blinding.
Simple math. Big savings. And zero arguments with your quantity surveyor later.
Estimating Your Materials
Blinding uses a simple mix — usually 1 : 3 : 6 (cement : sand : gravel). For every cubic meter of this mix, expect to use about:
- 7 bags of cement
- 0.42 m³ of sand
- 0.84 m³ of gravel
- ≈ 180 litres of water
For 4.2 m³ of blinding, multiply through:
- Cement → 30 bags
- Sand → 1.76 m³
- Gravel → 3.53 m³
Add a small margin (5–10 %) for uneven trenches. Trust me — it saves arguments when mixing starts.
Practical Site Tips
- Compact the trench base before pouring — don’t pour on soft ground.
- Blinding should follow excavation quickly, before soil slumps.
- Water the base lightly before placing concrete to reduce absorption.
- Always double-check with your site drawings before ordering materials.
On a real site in Ikeja, we once skipped that last check — ended up short by half a cubic meter. Lesson learnt.
Want to learn and understand how to handle cement calculations more? See our posts on how to calculate cement for differentpurposes.
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Join Intellect Architects — where design meets practical field knowledge. We blend classroom concepts with site experience so every architect, student, and builder can create better spaces.
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