Excavation Calculator

For a vertical-sided pit it is length × width × depth — but the length and width are the footing plus working space on every side, not the footing itself. With battered sides the hole is a frustum, and the volume comes from the prismoidal rule: (base area + top area + 4 × middle area) ÷ 6 × depth. Using average area × depth instead overstates a 1:1 battered pit by about 15%.

Because soil bulks up when it is disturbed. A cubic metre of common earth in the ground becomes about 1.25 m³ on the heap, clay about 1.35, and rock as much as 1.55. That swelled figure is what fills trucks, so it is what decides how many trips the spoil takes — while the excavation itself is measured and paid on the in-place volume.

300–600 mm on every side is usual. It is the room someone needs to stand in to fix shuttering against the footing and to strip it afterwards. Where the concrete is cast directly against the soil no working space is needed, but then the excavation has to be accurate to the footing line.

Broadly, beyond about 1.5 m with vertical sides — though it depends entirely on the soil, the water table and any load next to the hole. The alternative is battering the sides back to a safe slope, which costs volume instead of timber. Trench collapse is the most common fatal accident in construction and it happens without warning, so this is not a judgement to make by eye.

No. Both are priced separately and both vary enormously with the site. Hard rock usually needs a breaker or chiselling and is quoted at a different rate per cubic metre; dewatering depends on how much water arrives and how fast.