Outrigger Pad Size Calculator
An elevated work platform or crane is only as stable as the ground under its outriggers, and the pad is what spreads a concentrated stabiliser load out to a pressure the surface can actually carry. This calculator does the core arithmetic: it converts the maximum outrigger or stabiliser point load from your machine's manual or load chart, together with the allowable ground bearing pressure you hold for the site, into the pad area and minimum pad dimension you'd need — and it can also check the pressure a pad you already own would impose. It's built for EWP and MEWP owners, crane businesses, councils, government fleets, arborists and trades planning a set-up.
Both inputs must come from you. The point load belongs to your specific machine — read it from the load chart or the manufacturer's data, because it varies with boom position and configuration. The allowable bearing pressure belongs to your site and must come from a geotechnical report, the site engineer, or your own conservative judgement about the surface — it is not something this tool can supply, because it varies enormously between a concrete slab, compacted hardstand, topsoil, fill or ground near an excavation or service trench. This is a planning aid only: the ground assessment and the final pad choice are the competent person's and the engineer's call, and the machine's manual governs. If you want a hand, call 0416 689 689.
Enter Your Machine & Site Figures
Read this from your machine's load chart or manufacturer's data — use the worst-case configuration.
Must come from a geotechnical report, the site engineer, or a conservative competent-person assessment — never assumed.
Enter the side length of a pad you own to see the pressure it would impose.
Enter the point load and the allowable bearing pressure to size a pad.
How This Works & Assumptions
The calculation is the standard one for spreading a point load. Your outrigger or stabiliser applies a force to the ground; a pad spreads that force over an area, and the pressure the ground feels is the force divided by that area. Rearranged, the pad area you need is the force divided by the pressure the ground can safely carry. The tool converts your point load into a force (mass multiplied by gravitational acceleration) and divides it by the allowable bearing pressure you enter, giving the required area — then the minimum square side or round diameter that delivers it.
The point load is your machine's number. Read the maximum outrigger or stabiliser reaction from the load chart or manufacturer's data for your specific machine and configuration — it shifts with boom angle, slew position and the load being handled, so use the worst case for the set-up you're planning. Entering a rough guess here produces a rough answer.
The allowable bearing pressure is your site's number, and we deliberately do not supply one. Safe bearing pressure varies enormously — a sound concrete slab, compacted engineered hardstand, natural clay, loose fill, saturated ground and soil near the edge of an excavation or a buried service can differ by orders of magnitude. The only honest source is a geotechnical report, the site or structural engineer, or a genuinely conservative assessment by a competent person on the day. Never treat a number from the internet, including any example in a placeholder here, as a fact about your ground.
Optional pad check: if you already own a pad, enter its side length and the tool works out the pressure it would impose under your point load, so you can compare it against your allowable pressure. This is a first-pass check, not a sign-off.
Planning Aid — Not A Safety Guarantee
This calculator is a planning aid only. It does not assess your ground, account for punching shear, edge failure, slopes, voids, dynamic and eccentric loading, pad stiffness or the condition of the surface, and it never certifies a set-up as safe. The ground assessment and the final choice of pad, packing and set-up are the competent person's and the engineer's responsibility, and the machine's manual and load chart govern. When in doubt, stop and get engineering advice. Call 0416 689 689.
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