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The design lateral pressure the formwork must resist.
See the SCC Formwork Lateral Pressure Calculator, or your conventional-concrete ACI 347 pressure calculation. SCC is treated as fully hydrostatic over the whole pour height — about 23.6 kPa for every metre of wall — so a 10 m lift is already 236 kPa and a deep column pour runs higher still. Conventional concrete placed slowly enough for ACI 347's rate formula to apply comes out lower, but never above the same hydrostatic ceiling.
The tie's manufacturer-rated safe working load.
Use the manufacturer's rated capacity for your specific tie system, and check whether the figure quoted is already a safe working load or a breaking load — the safety factor below is applied to whatever you enter, so applying it twice divides the allowable load again for no reason, pulling your spacing in by a factor of one over the square root of the safety factor (about 29% tighter at the default 2.0, not the halving you might expect), and applying it to none at all removes it entirely. Light ties run from about 15 kN; heavy-duty wall and climbing systems are rated well past 100.
The safety factor applied to the tie's rated capacity.
2.0 is a commonly used formwork safety factor — check your project's formwork engineering requirements.
Maximum tie spacing
1.47 ft
This assumes a uniform square grid and uniform pressure across the form face — real formwork design must also check the sheathing and stud/waler capacity between ties, not just the tie spacing alone.
- Allowable tie load (after safety factor)
- 2.25 kips
- Tributary area per tie
- 2.15 sq ft
They open the calculator with your figures already in it
Concrete Formwork Tie Spacing Calculator: 1.47 ft — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
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How this was calculated
Formula source(s)
- Each form tie's tributary area = its allowable (safety-factored) load capacity / the fresh concrete lateral pressure; assuming a square grid, spacing = sqrt(tributary area)
Inputs used
- Fresh Concrete Lateral Pressure
- 1044.27 psf
- Form Tie Rated Capacity
- 4.5 kip
- Safety Factor
- 2
Intermediate steps
- Allowable tie load (after safety factor)
- 2.25 kips
- Tributary area per tie
- 2.15 sq ft
Confidence note: This assumes a uniform square grid and uniform pressure across the form face — real formwork design must also check the sheathing and stud/waler capacity between ties, not just the tie spacing alone.
What this calculation does not cover
- Only the ties are checked. The sheathing's bending and deflection, and the stud and waler spans between ties, are separate calculations, and on ordinary ply-and-timber forms one of those usually governs before the tie capacity does. Treat this spacing as a ceiling, not a layout.
- One pressure is applied over the whole form face. Pressure builds with depth, so a grid set from the base figure is conservative near the top, and a grid set from an average over the height is unsafe at the bottom, which is where a form bursts. Nothing here zones the wall or opens the grid up as it rises.
- The tributary area is that of a tie in the middle of a continuous grid. Ties at the ends and edges of a panel, at corners, and around blockouts and penetrations pick up more than their square share, and no allowance is made for them. It also ignores where a system panel's tie holes and walers actually fall, so the buildable spacing is the next hole position below this figure.
- The capacity you enter is the tie's, not the assembly's. Waler brackets and bearing plates, the cone, washer or wedge at the form face, thread engagement on she-bolts and taper ties, and a tie anchored back into a previous pour can each be weaker than the tie itself, as can a tie that has been reused, bent or corroded.
- Only the concrete's lateral pressure is resisted here. Wind on the form face, surcharge and impact from placing equipment, over-vibration, and eccentric or single-sided pours are carried by the bracing and by the form's own design, and none of them enter this arithmetic. This is a check on one component, not a formwork design — that belongs to a competent formwork designer.
Computed in your browser — nothing you enter is uploaded. Presented in US customary units and US trade terminology. Where a formula follows a published standard, that standard and its edition are cited beside it on this page; where none governs, the page says so. Local amendments override model codes — verify against the code in force where you build.
Sources checked 2026-09-06 · in the site-wide review of 2026-09-06 · v1.0.1
Regulatory standards & verification citations1
- Each form tie's tributary area = its allowable (safety-factored) load capacity / the fresh concrete lateral pressure; assuming a square grid, spacing = sqrt(tributary area)
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