Shed Base Slab Calculator

About this calculator

A shed base slab needs two volumes calculated separately: the concrete slab itself (base area × slab thickness) and the hardcore or MOT sub-base laid beneath it for drainage and load-bearing support (base area × sub-base thickness), since the two layers typically use different thicknesses and materials. Both are simple prism volumes, but getting the sub-base thickness right matters for how well the slab drains and resists frost heave over time.

DIY builders and small contractors run this calculation before ordering ready-mix concrete or bagged materials, since concrete is sold by volume and getting it wrong means either an under-strength pour that needs topping up mid-job or an expensive surplus. It also lets you compare the cost of a full concrete slab against lighter alternatives like a paving-slab or timber base for a given shed size.

This calculator takes your base dimensions and both layer thicknesses, and returns the concrete and hardcore volumes needed.