CHB / Hollow Block Calculator Philippines: How Many Blocks Do You Need? (Free Calculator)

Hollow concrete blocks (CHB) are the most common building material for walls in the Philippines — from bahay kubo extensions to commercial buildings. But calculating the exact number of CHBs needed is something most homeowners leave entirely to their contractor, often resulting in either running short (causing delays) or buying far too many (wasting thousands of pesos). This guide teaches you to calculate it yourself, and gives you a free tool to do it instantly.

Standard CHB Sizes in the Philippines

• 4-inch CHB (4×8×16 inches): Lightest, for non-load-bearing interior walls and fences. ≈₱15–₱22 per piece (2026)
• 6-inch CHB (6×8×16 inches): Most common for exterior walls and light load-bearing applications. ≈₱18–₱28 per piece
• 8-inch CHB (8×8×16 inches): For heavier load-bearing walls, retaining walls, and structural applications. ≈₱25–₱38 per piece

How Many CHBs Per Square Meter?

A standard CHB is 16 inches × 8 inches (approximately 40cm × 20cm). Each block covers 0.08 square meters of wall area. This gives a theoretical 12.5 blocks per square meter. In practice, accounting for mortar joints (approximately 10mm thick), the coverage is approximately 12 blocks per square meter for a single wythe (one block thick) wall.

Mortar Materials Required

Mortar is needed to bond CHBs together and fill the hollow cores for reinforced walls. As a rule of thumb, you need approximately 1 bag of Portland cement per 50 CHBs laid, plus 0.5 cubic meters of washed sand per bag of cement. For a reinforced wall (with steel bars and concrete fill in the cores), add 30% more cement and aggregate.

Step-by-Step Manual Calculation

1. 1Measure wall length (m) × wall height (m) = gross wall area (sqm)
2. 2Subtract door openings: each standard door = 0.8m × 2.1m = 1.68 sqm
3. 3Subtract window openings: each standard window = 1.2m × 1.0m = 1.2 sqm
4. 4Net wall area = gross area - total deductions
5. 5Base CHB count = net area × 12 blocks/sqm
6. 6Add wastage: multiply by 1.10 (10% for standard walls)
7. 7Round up to nearest whole number
8. 8Cement bags = total CHBs ÷ 50
9. 9Sand = cement bags × 0.5 cu.m.