About this calculator
This calculator turns a strip foundation's outline into a formwork (shuttering) take-off — boards stacked in courses to the required height, plus the stakes, braces, ties and fixings that hold the boards in place while the concrete cures. Enter the outline as a rectangle or as a list of straight runs, and say whether it forms a closed loop (no open ends) or an open run (two end panels needed).
Formula
total length = 2 x (length + width) [rectangle]
= sum of entered run lengths [list]
area = 2 x total length x height [both faces]
+ 2 x width x height (only if not a closed loop) [two end panels]
courses = ceil(height / board width)
boards per face per course = ceil(run length / stock board length)
boards (net) = 2 x boards-per-course x courses [+ end-panel boards if open]
boards (to buy) = ceil(boards net x (1 + waste%))
hardware run = 2 x total length [+ 2 x width if open]
stakes = ceil(hardware run / stake spacing) + 1
braces = ceil(hardware run / brace spacing) + 1
ties = courses x (ceil(total length / tie spacing) + 1)
fixings = boards (to buy) x fixings per board
Each course is cut from stock boards independently of the others — a simpler, always- sufficient model than optimally staggering joints between courses, so it can round a board up occasionally where a fuller packing might not.
Worked example
Defaults: a closed 6 x 8 m rectangular strip, 500 mm high, 200 mm wide boards in 4 m stock lengths, 10% waste, stakes/ties every 800 mm, braces every 2 m, 6 fixings per board.
total length = 2 x (6 + 8) = 28 m
area = 2 x 28 x 0.5 = 28 m²
courses = ceil(500 / 200) = 3
boards per face per course = ceil(28 / 4) = 7 -> net = 2 x 7 x 3 = 42 -> +10% = 47 boards
hardware run = 2 x 28 = 56 m
stakes = ceil(56/0.8) + 1 = 71; braces = ceil(56/2) + 1 = 29
ties = 3 x (ceil(28/0.8) + 1) = 108; fixings = 47 x 6 = 282
FAQ
Why does a closed loop need no end panels? A closed rectangular (or other closed) outline has no open end — the two long faces meet the two short faces at the corners, so there is nowhere for an "end" panel to go. An open run (a single straight or L-shaped stretch that stops rather than closing back on itself) has two open ends, each needing a panel the width of the strip to hold the concrete in.
Does this check whether the boards can resist the pressure of wet concrete? No. This is a geometric take-off only — it does not check board deflection, stake or brace spacing against the pour rate or concrete pressure, or tie strength. Those are a formwork design question for a competent person on site, not something this calculator verifies.
Why is the board count sometimes higher than I'd expect? Each course is cut independently, so a run that doesn't divide evenly into stock lengths rounds up separately in every course rather than being optimally staggered across them. This is a deliberate simplification (see the Formula section) — it never under-orders, but can occasionally over-order compared to a full cutting-diagram optimisation.
Which standard does this follow? None is cited. This is a plain geometric and spacing-based quantity take-off for temporary formwork, not a structural design calculation with a code basis.
Assumptions and limits
Board width/thickness, stock length, stake/brace/tie spacing and fixings-per-board are all user inputs with example defaults, not data for any specific product. Stake, brace and tie counts use straightforward spacing arithmetic (run length / spacing, plus one), not a wind, pour-rate or concrete-pressure calculation. The section drawing is schematic: it shows the two form faces and their separation, not real board joints or hardware positions.