Loan Concrete Block Fill Estimator
Block walls get their strength from what you pour into them — and "a yard or two" is how walls end up half-filled when the truck leaves. Enter the block count, size and fill pattern: get the core-fill yards before the pour, not during it.
Don't know the block count yet? The Concrete Block Estimator counts blocks and mortar for any wall — run it first, then bring the count here. Horizontal bond beams add fill too: roughly one filled course's worth per beam course.
How it works
Core volume scales with block width. The planning figures used across the industry (and by ready-mix drivers): filling every core takes about 0.55 cu yd per 100 blocks for 6-in block, 1.00 for 8-in, 1.45 for 10-in and 1.95 for 12-in. Filling every other core halves the per-core share; every third takes a third. Bags assume an 80-lb bag yields about 0.6 cu ft mixed — which is why anything past a yard is a ready-mix conversation, not a bag conversation.
Formula & worked example
Formula: Fill yards = blocks ÷ 100 × the planning rate for the block size (6 in: 0.55, 8 in: 1.00, 10 in: 1.45, 12 in: 1.95 cu yd per 100 blocks) × the pattern fraction (every core 1.0, every other 0.5, every third ⅓). 80-lb bags at 0.6 cu ft mixed each.
Worked example: 198 eight-inch blocks with every core filled: 1.98 cu yd of grout — about 90 eighty-pound bags, which is why core fill is normally a truck pour.
When to use this
- You are grouting CMU cores and ordering from a ready-mix plant.
- A wall spec calls for filled cores at set spacing and you need the yards.
- You are deciding between bags and a truck for a small fill job.
How to use it, step by step
- Get the block count (the Concrete Block Estimator counts any wall).
- Pick the block width — 8 in is the residential standard.
- Pick the fill pattern from the structural drawings.
- Order the yards shown, plus a quarter-yard cushion on truck pours.
What the inputs mean
| Input | What it is | Typical values |
|---|---|---|
| Block count | Total CMU in the wall | From the block estimator or the pallet count |
| Block size | Nominal block width | 6, 8, 10 or 12 in |
| Fill pattern | Which vertical cores get grout | All cores; every other (24 in o.c.); every third (32 in o.c.) |
Another worked example
100 twelve-inch blocks with every other core filled: the rate for 12-in block is 1.95 cu yd per 100 with all cores filled, halved by the pattern to 0.98 cu yd — about 44 eighty-pound bags if you insist on mixing, or a straightforward one-yard truck call with room to spare.
Frequently asked questions
How much concrete fills 100 8-inch blocks?
About 1.00 cu yd with every core filled — 0.50 yd filling every other core, 0.33 every third. In bags that full yard is roughly 45 eighty-pound bags, which is why core fill is normally a ready-mix or grout-pump job.
How many bags to fill 198 blocks?
The default wall here — 198 eight-inch blocks, every core: 1.98 cu yd, or about 90 eighty-pound bags. Two yards from a truck costs less than the bags and pours in minutes instead of a weekend.
Which cores actually need filling?
Cores holding vertical rebar, cores at openings and corners, and bond-beam courses — the pattern comes from the structural drawings. Decorative and garden walls are often filled only where steel sits; a retaining or load-bearing wall may spec every core.
Grout or concrete in the cores?
Grout — it is mixed wet and fine specifically to flow around rebar and fill webs completely. Standard concrete with coarse aggregate bridges and leaves voids. This estimator sizes the volume; the material choice belongs to the spec.
Does the mortar count change the fill?
Barely — joints sit between blocks, not in cores. The block estimator's mortar figure and this fill figure are separate purchases for the same wall.
▦ Need the block count first?
The Concrete Block Estimator counts CMU and mortar bags for any wall — then bring its block count back here for the fill.
How much grout for bond beams?
A filled bond-beam course takes roughly the all-cores rate for one course's worth of blocks. Add a course-equivalent per beam course to the vertical-fill figure when the wall has both.
Can I fill cores with a standard concrete truck mix?
Plants supply a dedicated grout/fill mix with smaller aggregate and high slump for core filling — order it by that name. Standard ¾-in aggregate mix bridges in 8-in cores and leaves voids around the steel.