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Acrow Prop Spacing Calculator — How Many Acrow Props Do I Need?
Calculate the number, spacing and size of Acrow props needed for temporary structural support when removing walls or installing steel beams.
Width of the opening being formed
Floor-to-ceiling height where props are installed
Number of floors above the opening
Max spacing between needle beams (default 1.2 m)
Safety notice
Structural elements must be designed or checked by a structural engineer before construction. Treat these figures as initial guidance for planning and budgeting, not a structural design.
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How We Calculate This
This calculator determines the number of Acrow props, their spacing, and the correct prop size based on the opening width, wall type, floor type, and number of floors being supported. It also calculates needles, strongboys, and sole plates needed.
Spacing guidelines (rule of thumb)
The figures below are a conservative trade rule of thumb, a starting point only. They are notderived from a code table. BS 5975 requires temporary works to be designed to the actual loads, so the real spacing must come from the structural engineer's temporary works design for your specific wall and floor loads.
- Load-bearing, timber floor: typically no more than 600mm centres
- Load-bearing, concrete floor: typically no more than 450mm centres
- Non-load-bearing: typically up to 900mm centres
- Multiple floors supported: reduce to 450mm or 300mm centres, and use needle beams, not Strongboys
Prop sizing and safe working load
The height ranges below are the BS 4074:1982 closed-to-extended ranges. The safe working load (SWL) of an adjustable steel prop is governed by how far it is extended, not by its size number, and it falls sharply as the prop is extended. The SWLs quoted are from CIRIA Technical Note 79 (1977) for the eccentric loading case (25mm eccentricity, 1.5° out of plumb). This is the case that applies when propping masonry or timber bearers where concentric loading cannot be guaranteed.
- Size 0: 1040-1829mm
- Size 1: 1753-3124mm
- Size 2: 1981-3352mm
- Size 3: 2591-3962mm
- Size 4: 3200-4877mm
SWL (eccentric, sizes 0–3): ≈ 17 kN up to 2.75 m extended, then ≈ 15 kN at 3.0 m, 13 kN at 3.25 m, 11 kN at 3.5 m and 10 kN at 3.75 m. Size 4: ≈ 17 kN at 3.25 m falling to ≈ 7 kN at 4.75 m. Where concentric loading can be guaranteed (e.g. fork heads / proper formwork) the SWL is higher. Always read the value from the prop maker's load table at the actual extension.
Important notes
This calculator provides general guidance only. Temporary works design must be carried out or verified by a competent person (structural engineer or temporary works coordinator). This must be done in accordance with BS 5975-1:2024 (management procedures for the control of temporary works) and BS 5975-2:2024 (falsework: design and implementation). Every structural alteration is unique and must be assessed individually.
Standards
Acrow prop use should comply with BS 5975-1:2024 and BS 5975-2:2024 (Temporary works) and BS EN 1065 (Adjustable telescopic steel props; props are also marked to the older BS 4074:1982). The structural alteration itself requires Building Regulations approval and a structural engineer's design to comply with Approved Document A (Structure).
Frequently Asked Questions
Acrow prop spacing depends entirely on the load being supported, so there is no single code figure. As a conservative trade rule of thumb, load-bearing walls with timber floors above are propped at no more than about 600mm centres. Concrete floors or multiple storeys need 450mm or even 300mm centres, and non-load-bearing walls can go up to 900mm. These are starting points, not code-derived limits. BS 5975 requires temporary works to be designed to the actual loads, so always follow the structural engineer's specification. They will calculate the exact loads and required prop spacing for your specific situation.
Acrow props come in sizes 0-4. Size 0 covers 1040-1829mm (low rooms, basements), Size 1 covers 1753-3124mm (standard rooms), Size 2 covers 1981-3352mm, Size 3 covers 2591-3962mm (high ceilings), and Size 4 covers 3200-4877mm (commercial). For standard UK ceiling heights of 2.4m, Size 1 props are typically used. The prop should never be extended more than two-thirds of its adjustment range, as this reduces its safe working load.
A Strongboy is an L-shaped attachment that fits on top of an Acrow prop and slides into a mortar joint in brickwork or blockwork. It supports the masonry above while the wall below is removed (for example, when installing a new opening or lintel). A Strongboy has a safe working load of only 340 kg (about 3.34 kN) per unit (BS 4074:1982) and should be spaced no more than 900mm apart. Strongboys are only suitable for single-storey masonry support and must not be used where the wall supports more than one floor. For heavier or multi-storey loads, needle beams are used instead. See our Lintel Sizing Calculator for the permanent support design.
Yes, you should always consult a structural engineer before removing any wall, even if you believe it is non-load-bearing. The engineer will assess the loads, specify the correct steel beam or lintel, and provide a temporary works design including prop spacing and sequencing. Building Regulations approval is required for any structural alteration. The engineer will typically provide a specification drawing that your builder follows during the work.
Sole plates are timber boards (typically 225x50mm or similar) placed under the foot of each Acrow prop to spread the load over a larger area of floor. Without a sole plate, the concentrated point load from the prop can damage or punch through a timber floor, or crack floor tiles. The sole plate should span across at least two floor joists (for timber floors) and extend at least 150mm beyond the prop base on each side.
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Last updated: February 2026
Verified against UK standards · estimates only, confirm with your supplier.