Preliminary strip, pad and raft sizing from the soil capacity you supply.
Foundation, roof and structure. 5 questions answered below, each with the arithmetic behind it and the limits of what the tool decides. Open the Foundation Designer tool.
A footing size is the product of a load and a ground condition, and both have to come from somewhere. This tool takes the load you enter, the bearing capacity you supply and the dimensions of the structure, and returns a footing size with the arithmetic shown, so the suggestion can be checked rather than believed. What it is not is a certified design. Bearing capacity comes from a soil report or a presumptive value for a known soil, and the value of that number is the whole value of the footing. Where it is unknown, the tool asks for it and stops. Where an engineer has specified a size, you enter it and the tool measures materials for that size instead.
A wall carrying ninety kilonewtons per metre on ground with a bearing capacity of a hundred kilonewtons per square metre needs nine tenths of a square metre of ground of footing for every metre of wall, so a width of nine hundred millimetres. At that width and two hundred and fifty deep, the footing is two point two five cubic metres of concrete over ten metres, before waste. Enter a bearing capacity of fifty instead and the width doubles, and the concrete with it. The same wall, the same load, half the ground capacity, twice the concrete, which is why the number cannot be assumed.
A suggested footing width with its calculation, the bearing pressure that width imposes, and the concrete and blockwork for the resulting dimensions. It also accepts a width you specify, in which case it measures rather than suggests. What it does not produce is a design certificate: the output is a material quantity attached to a sizing calculation that an engineer can check or replace.
From you, ideally from a soil report. Bearing capacity is a property of the ground, and presumptive values exist for known soils at known depths, but the honest source is a investigation. The tool will not invent one, because a footing sized on an assumed capacity is a footing whose safety depends on an assumption nobody has tested. Where the value is unknown, the calculation stops.
No. What it produces is a sizing calculation with a material quantity attached, which an engineer can check and either accept or replace. Certification involves the ground investigation, the structural design, the reinforcement and the professional's judgement about the specific site. Treat the output as a check on a proposal or a starting point for a conversation, not as a document that satisfies a building authority.
The foundation calculator measures materials for dimensions you already have. The designer starts one step earlier, from a load and a bearing capacity, and proposes dimensions before measuring them. Both end in concrete and blockwork quantities, and both state that reinforcement, excavation and design sit outside them. Use the designer when the footing size is still open, and the calculator when it is fixed.
Yes, and it is the intended path for anything serious. Enter the width an engineer has specified and the suggestion steps aside, with the quantities following your figure. That is what makes the tool useful alongside a design rather than in place of one: it takes the decision as an input and returns the material order that decision implies.