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Wall form pressure (ACI 347) = Cw·Cc·(150 + 9000R/T) psf for pour rates under 7 ft/h and walls up to 14 ft, at least 600·Cw psf and never more than full liquid head. A 3 m wall poured at 1.5 m/h at 20 °C gives about 38.4 kPa; 600 × 600 mm tie spacing then puts 13.8 kN on each tie.

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Geometry
m
m
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Concrete placement
m/h
°C
kg/m³
Formwork build-up
mm
mm
mm
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%
Wall formwork elevation12 m3 mWall form · 250 mm thickstudswalerstiesmyconstructioncalculator.com
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Results

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Facing sheets required
27sheets, 10% waste incl.
Contact area (both faces)72.0 m²
Stop-ends (both wall ends)1.5 m²
Concrete volume9.00 m³
Studs (each 3.0 m)62 pcs · 186.0 m
Waler length, total120.0 m (5 rows per face)
Form ties required100 pcs
Load per tie at peak pressure13.8 kN
Peak lateral pressure on formwork
38.4 kPa
54% of full hydrostatic pressure at this height: ACI 347 wall equation (R < 7 ft/h ≈ 2.1 m/h, h ≤ 14 ft ≈ 4.2 m).
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Working
  1. Cw = 1.000 (from density); Cc = 1.0; R = 4.92 ft/h; T = 68 °F
  2. ACI 347: p = Cw·Cc·(150 + 9000R/T) = 38.4 kPa
  3. Limits: minimum 600·Cw psf; maximum w·h = 70.6 kPa
  4. Design pressure = 38.4 kPa, reached 1.63 m below the top of the pour
  5. Contact area = 2 × H × L = 2 × 3.0 × 12.0 = 72.0 m²
  6. Sheets = ⌈72.0 × 1.10 ÷ 2.98 m²⌉ = 27
  7. Studs = (⌈L ÷ 400⌉ + 1) × 2 faces = 62
  8. Walers = ⌈H ÷ 600⌉ = 5 rows × 12.0 m × 2 faces = 120.0 m
  9. Ties = ⌈L ÷ 600⌉ × ⌈H ÷ 600⌉ = 100; load = 38.4 kPa × 600 × 600 mm = 13.8 kN
Results are estimates for planning and material ordering only. They are not a substitute for structural design or approval by a qualified engineer. Read the full disclaimer.
Formulas


Lateral pressure (ACI 347R-14, inch-pound units):


Walls, R < 7 ft/h and h ≤ 14 ft:      p = Cw · Cc · (150 + 9000 R / T)
Walls, h > 14 ft or 7 ≤ R ≤ 15 ft/h:  p = Cw · Cc · (150 + 43,400 / T + 2800 R / T)
Limits:                               600 · Cw ≤ p ≤ w · h
Walls, R > 15 ft/h, or SCC:           p = w · h


p in psf, R = rate of rise (ft/h), T = concrete temperature (°F), w = unit weight (lb/ft³), h = pour height (ft). 1 psf = 0.0479 kPa.


Material take-off (both faces):


Contact area = 2 × H × L                   Sheets = ⌈area × (1 + waste) ÷ sheet area⌉
Studs        = (⌈L ÷ stud spacing⌉ + 1) × 2  Walers = ⌈H ÷ waler spacing⌉ rows × L × 2
Ties         = ⌈L ÷ tie spacing H⌉ × ⌈H ÷ tie spacing V⌉
Tie load     = p × tie spacing H × tie spacing V


Worked example


A wall 10 ft high and 40 ft long, placed at 5 ft/h at 70 °F, normal-weight concrete (150 lb/ft³), Type I cement without retarder:


    

  1. Cw = 1.0, Cc = 1.0; the wall is under 14 ft and R under 7 ft/h, so the first equation applies
    2. 

  2. p = 150 + 9000 × 5 ÷ 70 = 793 psf (about 38 kPa)
    3. 

  3. Check the limits: 600 ≤ 793 ≤ 150 × 10 = 1,500 psf ✓: 53% of full liquid head
    4. 

  4. Ties at 24 × 24 in: 793 × 2 × 2 = 3.17 kips per tie
    5. 

  5. Contact area = 2 × 10 × 40 = 800 ft² → 28 sheets of 4 × 8 ft with 10% waste
    6. 



The same wall in metric (3 m high, 1.5 m/h, 20 °C) gives 38.4 kPa and 13.8 kN per tie at 600 × 600 mm.


How pour rate changes the pressure (3 m wall, 20 °C, normal concrete)






Pour rate
Design pressure
Share of full liquid head






0.5 m/h
28.7 kPa (minimum governs)
41%




1.0 m/h
28.7 kPa (minimum governs)
41%




1.5 m/h
38.4 kPa
54%




2.0 m/h
48.8 kPa
69%




3.0 m/h
57.1 kPa (second equation, R > 2.1 m/h)
81%




5.0 m/h
70.6 kPa (hydrostatic)
100%






Assumptions and limits


    

  • Placement from the top with normal internal vibration no deeper than 1.2 m (4 ft) into the previous layer.
    • 

  • Cw follows the concrete density: 1.0 between 2,240 and 2,400 kg/m³ (140–150 lb/ft³), lower for lightweight concrete (not below 0.8), higher for heavyweight.
    • 

  • Studs are counted at both ends of each face. Walers and ties are counted one per spacing band, and double walers need twice the length.
    • 

  • The calculator does not check plywood, stud or waler strength, deflection or bracing.
    • 



Frequently Asked Questions
How do you calculate concrete pressure on formwork?
Under ACI 347R-14, walls placed at under 7 ft/h (2.1 m/h) and no taller than 14 ft (4.2 m) use Cw·Cc·(150 + 9000R/T) psf, where R is the rate of rise in ft/h and T the concrete temperature in °F. Taller walls and faster pours up to 15 ft/h use Cw·Cc·(150 + 43,400/T + 2800R/T). The result is at least 600·Cw psf and never more than the full liquid head, density × height.
When should formwork be designed for full hydrostatic pressure?
For self-consolidating concrete, slumps over 7 in (175 mm), concrete pumped in from the bottom of the form, revibration deeper than 4 ft (1.2 m), wall pours faster than 15 ft/h (4.5 m/h), and whenever the equation gives more than density × height.
Why does temperature matter?
Cold concrete stiffens more slowly, so a taller column of it stays fluid and pushes on the form. Halving the temperature in °F roughly doubles the rate term of the equation.
How do I check if my ties are strong enough?
Multiply the design pressure by the area each tie supports (horizontal × vertical spacing). Compare that load with the tie's safe working load from the manufacturer, which includes a safety factor. Reduce the spacing if the load is too high.
Can I use this for the final formwork design?
No. It is for planning, comparing options and ordering materials. Formwork for the actual job must be designed and checked by a competent formwork or structural engineer, including plywood, stud and waler bending, deflection and bracing.
References
  • ACI 347R-14 Guide to Formwork for Concrete, §4.2 lateral pressure of concrete
  • CIRIA Report 108 is the common alternative in the UK; it gives different (often higher) values
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