How to Estimate Materials for Drywall and Blockwork Projects

By Timothy Kyalo – Construction PM | Site Supervisor | Mjengo Hub Member

Introduction: Why Accurate Estimation Matters

In the field, I’ve seen projects stall because of 10 missing boards or 100 extra blocks. Estimating materials accurately helps you control costs, reduce wastage, and improve workflow. In this guide, I’ll walk you through a simple process I use on-site to estimate drywall and blockwork materials—based on real project conditions in places like Nairobi and Ruiru.

Part 1: Estimating Drywall Materials

Step 1: Understand the Wall Design

• Wall thickness (e.g. 100mm using 67mm studs)
• Standard height (e.g. 3m) or as specified
• Stud spacing: usually 400mm or 600mm centers

Step 2: Measure Wall Area

Use the formula:

Wall Area = Length × Height

Example:
3.1m × 3m = 9.3m²
Repeat for all walls and sum them.

Step 3: Calculate Number of Gypsum Boards

Standard board size: 1.2m × 2.4m = 2.88m²

Boards Required = Total Wall Area ÷ 2.88

Add 10% for wastage.

Step 4: Estimate Framing Materials

• Vertical studs: At 400mm centers, roughly 2.5 studs per meter
  (Wall length × 2.5 = Number of studs)
• Top and bottom tracks: Equal to total wall length
• Add extra for openings and corners

Step 5: Screws, Joint Tape, and Compound

• Screws: 30–40 per board
• Joint tape: Equal to total seam length in meters
• Joint compound: 4–5 kg per 10 m²

Note: Always confirm whether the boards are installed vertically or horizontally. This affects joint placement and wastage.

Part 2: Estimating Hollow Block Wall Materials

Step 1: Measure Wall Area

Wall Area = Length × Height

Step 2: Know the Block Size

A standard hollow block (400mm × 200mm) covers 0.08m².
You’ll need approximately 12.5 blocks per square meter.

Step 3: Calculate Number of Blocks

Total Blocks = Wall Area × 12.5

Add 5–10% for cutting and wastage.

Step 4: Estimate Mortar Quantity

General rule:
1 bag of cement + 3 wheelbarrows of sand = mortar for 100 blocks

Example for a 5m x 3.8m wall (19 m²):

• Blocks: 19 × 12.5 = 238 → Round up to 250
• Mortar: About 2.5 bags of cement and 7.5 wheelbarrows of sand

Site-Based Practical Example

Drywall Calculation:

• Wall A: 2.8m × 3m = 8.4 m²
• Wall B: 3.2m × 3m = 9.6 m²
• Total Area = 18 m²
• Boards = 18 ÷ 2.88 = 6.25 → Round to 7 boards (with wastage)

Blockwork Calculation:

• Wall: 5m × 3.8m = 19 m²
• Blocks = 19 × 12.5 = 238 → Round to 250 blocks

These figures are pulled from actual jobs I’ve managed in fit-out works across Nairobi and Ruiru.

Tools That Can Help You Estimate Faster

• Laser measure or standard tape measure
• Excel or Google Sheets for recording and calculating
• Mobile apps like PlanSwift, BuildCalc, or MagicPlan

Conclusion: Start with Accuracy, End with Efficiency

Estimation is not guesswork. It’s a skill that can save money, time, and prevent mid-project delays. Whether you’re working on a single office partition or a housing block, taking the time to do proper calculations pays off.

If you’d like assistance estimating materials for your upcoming project, feel free to reach out through Fiverr or connect via Mjengo X.

Published by Timothy Kyalo – Construction Project Manager & Site Supervisor