Block Fill Grout Calculator
Cubic yards of grout to fill a block wall at your actual rebar spacing — with the bond beam counted, which is where most orders come up short.
1.33 yd³ neat plus 10% waste
Only 1.47 yd³. That is under most short-load thresholds, so either price the fee in or mix 66 bags on site — grout for a small wall is very often a bag job.
8 ft of wall. Most codes cap a grout lift at 5 ft unless the wall is built for high-lift grouting, so plan on 2 lifts with consolidation between them.
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How to work it out yourself
- 1
Wall area first, openings out
Length times height gives the gross face area, and you take the doors, windows and garage head out of it. A nominal 8 x 16 unit covers 0.889 sq ft, so there are 1.125 blocks to the square foot — 112 or 113 block per hundred square feet of wall, whatever the block width is. Width changes the grout, never the block count.
- 2
Grout per core, by block width
Filling both cores of a standard two-core unit takes roughly 0.20 cubic feet in a 6 in block, 0.30 in an 8 in, 0.42 in a 10 in and 0.52 in a 12 in. Those are typical rather than exact: web thickness is not standardised between plants, and a few percent either way is normal. Ask your block supplier for their own figure if you are pouring a lot of wall — on a big job the difference is a truck.
- 3
Then only the cells you actually grout
This is the step every rule of thumb skips. Cores sit 8 in apart in a 16 in unit, so grouting at 16 in on center fills half of them, 32 in fills a quarter and 48 in fills a sixth. The familiar “about 1.1 yards per hundred block” figure assumes a solid grouted wall. Apply it to a wall reinforced at 32 in and you have ordered four times what the drawings call for.
- 4
Add the bond beam separately
A bond beam is a horizontal course grouted end to end, and it follows the wall rather than the coursing — so it is priced per lineal foot, not per block. Roughly 0.22 cubic feet per lineal foot in an 8 in wall. There is almost always one at the top of the wall and a lintel course over every opening, and on a low wall those courses can be a quarter of the whole order.
- 5
Waste last
Ten percent is the usual allowance and it is not padding. Grout is a wet mix, some of it stays in the pump line and the hopper, some fills the odd broken web you cannot see, and cleaning out mid-pour is not an option once you have started a lift.
Worked example: A 40 ft x 8 ft wall, 8 in block, #5 at 32 in o.c., one bond beam
| Wall area | 40 ft × 8 ft = 320 sq ft |
| Block | 320 × 1.125 = 360 block |
| Cores grouted | 8 ÷ 32 = one core in four |
| Vertical grout | 360 × 0.30 × 0.25 = 27.0 cu ft |
| Bond beam | 40 lf × 0.225 = 9.0 cu ft |
| Neat total | 36.0 cu ft ÷ 27 = 1.33 yd³ |
| Plus 10% waste | 1.47 yd³ — order 1.5 |
| Or bagged | 66 × 80 lb bags |
Grouted solid instead, the same wall takes 4.77 yd³. That gap — three and a third yards on one modest wall, and it scales — is the entire reason this calculator asks for the spacing before it gives you a number.
Order grout, not concrete, and watch the lift height
Grout is a separate product: a wetter mix with pea gravel or no coarse aggregate at all, slumped 8 to 11 in so it flows into a core and around a bar. A standard slab mix will bridge partway down a cell and leave a void you cannot see, cannot test and cannot fix once the wall is capped. And most codes cap a single grout lift at about 5 ft unless the wall is detailed for high-lift grouting with cleanouts at the base — an 8 ft wall is two lifts with consolidation between them, which is a scheduling fact as much as a code one. Plan the truck around it before it turns up.
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Common questions
How much grout do I need to fill an 8 inch block wall?
Grouted solid, an 8 in block takes about 0.30 cubic feet, which is roughly 1.1 cubic yards per 100 block or 1.25 yd³ per 100 sq ft of wall. Grouted only at reinforced cells it is far less: a quarter of that at 32 in on center, a sixth at 48 in.
How many blocks are in 100 square feet of wall?
About 113 — a nominal 8 x 16 unit covers 0.889 sq ft, so 1.125 blocks per square foot. That is the same for 6, 8, 10 and 12 in block, because the face dimension does not change with the width.
Do I have to fill every core in a block wall?
Only if the drawings say so. Most reinforced walls grout the cells containing vertical bar and nothing else, commonly at 32 or 48 in on center. Fully grouted walls are specified where the wall carries real load, retains soil, or sits in a high-wind or seismic zone — read the structural sheet rather than assuming either way.
Can I fill block with regular concrete mix?
It is a bad idea. Coarse aggregate bridges in a 5 in cell and leaves voids around the bar, which is exactly where the strength was supposed to be. Use a proper grout mix at 8 to 11 in slump, or a fine grout for cells under 2 in wide.
How many 80 lb bags of grout fill a block?
An 80 lb bag yields about 0.6 cubic feet, so one bag fills two 8 in block solid, or one 12 in block with a little left over. Bagging is realistic under about two yards — past that you are mixing all day for the price of a short-load fee.
What is a bond beam and does it change the grout order?
It is a horizontal course of channel-shaped block grouted end to end with bar in it, tying the wall together at the top and over openings. It always adds grout, roughly 0.22 cubic feet per lineal foot in an 8 in wall, and forgetting it is the most common reason a grout order arrives short.
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Free to use anywhere — a supplier’s resources page, a builder’s blog, a trade forum answer. It works on a phone, needs no account from your visitors, and we will not change it out from under you. All we ask is that you keep the credit line underneath, which is the second half of the snippet.
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