The concrete is the core, not the wall
This is the one error worth designing a page around. An ICF block is foam either side of a cavity, and the cavity is what gets filled. A six inch core with two and a half inches of foam on each face makes an eleven inch wall, and eleven divided by six is 1.83. Order against the wall thickness and you are 83 percent over on the largest single line item on the job.
The reason it happens is that the two numbers live in different places. The overall thickness is what appears on the plan, in the wall schedule and in every conversation about the building. The core thickness is a property of the block, buried in a specification sheet, and it is the only figure a concrete order should ever see. The calculator prints both, side by side, with the percentage between them, so the mistake is visible rather than latent.
Blocks and concrete do not talk to each other
Block count comes from the face of the block covering the face of the wall: face length into the run gives blocks per course, face height into the height gives courses, and the product is the layout. Concrete comes from the net face area times the core. Change the core thickness and the concrete moves and the block count does not move at all, because a wider block still shows the same face to the wall.
That independence is worth knowing when a structural change lands late. Going from a six inch core to an eight inch core is a different block and a different concrete order, but it is the same number of blocks and the same number of courses, so the layout, the bracing positions and the schedule barely move.
Corners are counted per course, and the run is measured between them
Every corner takes a corner block in every course. Twelve courses and four corners is 48 corner blocks, and they are a different item at a different price. The trap is double counting: if you measure your straight runs right through the corners and then add corner blocks on top, you have paid for the corner twice. Measure the runs between corners, as this page asks, and the two counts do not overlap.
What is deliberately absent
No core size, no rebar, no lift height, no bracing spacing, no R-value, no view on whether any of the numbers you entered suit the wall. Core thickness and reinforcement come off the structural drawings. Lift height is a form pressure decision that depends on the placement rate and the concrete temperature far more than on the wall, and it belongs to the block manufacturer and the engineer of record. The bracing layout comes from the bracing supplier.
An ICF pour is a form failure risk like any other wall pour, with the added feature that the form is foam. A blowout releases the fluid head at once and people have been killed under collapsed forms and shoring. Wet concrete burns skin chemically over a period of hours rather than announcing itself on contact. Both are stated here and neither is procedure.
Questions people ask
How much concrete does an ICF wall take?
Net wall face area times the core thickness, and nothing else. On the defaults here — 120 feet of run at 9 feet high with six 4 by 4 foot openings and a 6 inch core — that comes to 18.22 cubic yards before waste and 19.13 with a five percent allowance. Using the overall 11 inch wall thickness instead would put the order 83 percent over. The core figure is in the block specification, not on the plan.
Does a thicker core mean more blocks?
No. The block face still covers the same amount of wall, so the course count and the blocks per course do not change when the core does. Only the concrete moves, and by the ratio of the two core thicknesses. That is useful when a structural change arrives late, because the block order, the layout and the bracing positions all survive it.
How do I count corner blocks without double counting?
Measure the straight runs between the corners rather than through them, and count one corner block per corner per course. This page is set up that way. If you measured your runs to the outside of the building instead, the straight block count is high by roughly one corner block length in every course, at every corner.
What lift height should I pour in?
Whatever the block manufacturer and the pour plan say, and this page supplies no figure. Lift height exists to keep the lateral pressure within what the form can take, and that pressure depends on how fast the concrete rises and how warm it is rather than on the wall itself. The form pressure calculator on this site works that arithmetic on coefficients you supply.
How many braces does an ICF wall need?
That comes from the bracing supplier layout for your wall height and your pour, and this page turns the spacing you were given into positions along the run. It does not tell you what the spacing should be. Corners, openings and the top course generally take extra beyond whatever the regular spacing is, and how the braces are anchored matters as much as how many there are.