About this calculator
This calculator works out the materials for a dug (shaft) well lined with precast concrete rings: how many rings, their mass for lifting and transport, the gravel filter or base slab at the bottom, the cover slab with its hatch, how much soil to dig out and backfill, and how much water one metre of water column holds.
The rings stand on the bottom of the pit — with a gravel filter inside the bottom ring — or on a concrete base slab, and rise to the well head above ground. Rings come in whole heights, so the count is rounded up and the calculator shows how high the head actually ends up.
The defaults are typical Lithuanian manufacturers' catalogue figures: internal diameters of 0.7, 1.0, 1.5 and 2.0 m, 1 m high rings with a 90 mm wall, and a 150 mm cover slab with a 700 mm hatch. Use your supplier's data — ring heights, joints and masses differ between products.
Formula
outer diameter = internal diameter + 2 × wall
rings = ceil((depth + head − base slab) / ring height)
actual head = rings × ring height + base slab − depth
ring concrete = π/4 × (outer² − internal²) × ring height
ring mass = ring concrete × density
gravel filter = π/4 × internal² × filter thickness
base slab = π/4 × outer² × slab thickness
cover slab = π/4 × (outer² − hatch²) × cover thickness
pit diameter = outer diameter + 2 × working gap
excavation = π/4 × pit diameter² × depth
backfill = π/4 × (pit diameter² − outer²) × depth
water per metre = π/4 × internal² × 1 m
Worked example
A 6 m deep well, 1.0 m rings 1000 mm high with a 90 mm wall, head 800 mm above ground, a 200 mm gravel filter, 2450 kg/m³ concrete, a 300 mm working gap:
outer diameter = 1000 + 2 × 90 = 1180 mm
rings = ceil((6000 + 800) / 1000) = 7 (head ends 1000 mm up)
ring concrete = π/4 × (1.18² − 1.00²) × 1.0 = 0.308 m³
ring mass = 0.308 × 2450 = 755 kg
gravel filter = π/4 × 1.0² × 0.2 = 0.157 m³
cover slab = π/4 × (1.18² − 0.70²) × 0.15 = 0.106 m³ → 260 kg
excavation = π/4 × 1.78² × 6 = 14.9 m³
water = π/4 × 1.0² × 1 = 785 L per metre
The 755 kg ring matches the catalogues: 759 kg and 740 kg for 1.0 × 1.0 m rings with a 90 mm wall from two Lithuanian manufacturers.
FAQ
Gravel filter or base slab? A drinking-water well takes its water through the bottom, so it usually gets a gravel filter inside the bottom ring. A base slab closes the bottom — used where the water comes through the walls or the well is a storage or inspection shaft.
Why does the head end up higher than I entered? Because rings come in whole heights. Most manufacturers also make shorter rings (250, 500, 750 mm); use one at the top to hit the height exactly.
Is the excavation volume what the truck takes away? No — it is the volume of soil in the ground. Dug soil bulks up; use the excavation calculator to estimate the loose volume. If the rings are sunk as the shaft is dug, set the working gap to 0.
How high should the well head be above ground? High enough to keep surface water and debris out, with a clay seal around it. We did not verify a Lithuanian rule for the minimum height, so the 800 mm default is only an example — check the rules that apply to your well.
Does the calculator say where to put the well? No. Distances from septic systems, toilets and plot boundaries and the water quality are separate matters.
Assumptions and limits
No standard is cited: the arithmetic is cylinder volumes and counting, and the ring sizes are manufacturers' products.
Defaults to replace: 6 m depth, 800 mm head, 1.0 m × 1000 mm rings with a 90 mm wall, 2450 kg/m³ (back-calculated from the catalogue masses), 200 mm filter or 100 mm slab, 150 mm cover with a 700 mm hatch, 300 mm working gap.
Geometry: plain cylindrical rings stacked straight; rebates, ladders, cast bottoms, sealing mortar or joint seals, the clay seal around the head and the hatch lid itself are not counted. The pit is a vertical cylinder; sloped sides or shoring are not modelled.