Concrete Block Fill Calculator
How much grout or concrete it takes to fill the cores of a block wall — for reinforced or partially filled blockwork.
Grout to fill the hollows in a block wall.
How the concrete block fill calculator works
A hollow block is roughly 50% void. Filling every core in a standard 390 × 190 × 190 block takes about 0.0070 m³ — seven liters — so a square meter of fully grouted wall needs about 0.088 m³.
Most walls are only partially filled — every second or third core, wherever a reinforcing bar goes. Setting the fill spacing here is what separates a realistic order from a wildly over-specified one.
Formula: grout = filled cores × core volume
Worked examples
| Inputs | Grout volume | Note |
|---|---|---|
| Fully grouted 10 × 2.4 m wall | 2.482 | about 2.3 m³ with waste |
| Every 3rd core | 0.827 | a third of the grout |
| A small retaining wall | 0.31 | about 0.3 m³ |
FAQFrequently asked questions
How much grout fills a block?
About 0.0070 m³ for a standard 390 × 190 × 190 block with both cores filled — roughly seven liters, since the block is around half void.
Do I need to fill every core?
Only where the engineer says so. Most walls are filled at reinforcement spacing — every second, third or fourth core.
What mix should I use?
A high-slump grout, not standard concrete. It has to flow into narrow cores without segregating, which usually means a smaller aggregate and more water plus a plasticiser.
Why such a large waste allowance?
Because grout spills, blocks are broken, and cores are rarely as clean as the calculation assumes. Ten per cent is standard.
Can I pour it all at once?
No — grout in lifts, typically no more than 1.2 to 1.5 m at a time, or the pressure blows out the joints.
Where these figures come from
- The Engineering ToolBox — material densities, coverage and unit data — bulk densities, concrete at 2,400 kg/m³, board and sheet sizes
- Gypsum Association — gypsum board sizes — 4 × 8 and 4 × 12 ft sheets
- ADA Standards for Accessible Design — ramps (§405) — maximum running slope 1:12
- International Code Council — the International Residential Code
Last checked: September 2026. Coverage rates and material sizes are typical manufacturer figures — check the product you buy.