How many piles do I need?

The number of piles = Total Building Load / (Pile Working Capacity / Safety Factor). The safety factor is typically 2.0-2.5 for piles. For a 500 kN total load with 250mm CFA piles (200 kN ultimate capacity), factored capacity = 80 kN, so you need approximately 7 piles. The structural engineer determines the exact count and positions.

What is the minimum pile spacing?

Piles should be spaced at a minimum of 3 times the pile diameter centre-to-centre. For 250mm piles, minimum spacing is 750mm. For 450mm piles, it's 1.35m. Closer spacing causes stress overlap in the soil, reducing the capacity of each pile. In practice, pile positions are determined by the building layout and load paths.

What are ground beams?

Ground beams are reinforced concrete beams that span between pile caps, supporting the building walls above. They transfer wall loads to the piles. Typical domestic ground beams are 450-600mm deep × 300-450mm wide with rebar reinforcement. They sit on a compressible material (e.g., Clayboard) so they can move independently of the soil.

When are piled foundations needed?

Piled foundations are used when the soil near the surface cannot support the building loads — for example, soft clay, made ground, peat, or areas with large trees causing clay shrinkage. They transfer loads through weak soil to a stronger stratum below. Common in the UK for sites with significant tree influence on shrinkable clay.

How much do piled foundations cost?

Mini-piles (150mm) cost approximately £800-1,500 each. CFA piles (250-300mm) cost £1,000-2,000 each. The rig mobilisation/demobilisation is typically £1,000-3,000 regardless of the number of piles. Ground beams add £80-150 per linear metre. A typical domestic piling scheme (15-25 piles + ground beams) costs £15,000-40,000.

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Pile Foundation Calculator — Pile Count, Spacing & Ground Beams

Calculate pile count from total building load and capacity, minimum spacing, and ground beam requirements.

Total Building Load

Total factored load from structure

Pile Diameter

Capacity: 200 kN ultimate

Pile Length

Depth to bearing stratum

Pile Price

Ground Beam Length

Total ground beam run

Ground Beam Price

How We Calculate This

This calculator estimates the number of piles needed based on total building load and individual pile capacity, plus ground beam quantities.

Pile count

Factored Capacity = Ultimate Capacity / Safety Factor
Piles = ceil(Total Load / Factored Capacity)
Safety factor typically 2.0-2.5 for piles.

Spacing

Minimum Spacing = Pile Diameter × 3
Ground beams span between pile caps to support wall loads above.

Frequently Asked Questions

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Last updated: March 2026

All calculations are estimates. Verify with your supplier.