TryBuildCalcPile Foundation Steel Calculator Pile reinforcement estimator
Calculate concrete and steel quantity for a group of bored or driven cast-in-situ pile shafts.
🕒 Last updated: August 13, 2026
Pile Dimensions
ℹ️How many identical piles in this group — the final quantity is the sum across all of them.
ℹ️Depth of the pile shaft below cut-off level, from the soil report / structural drawing.
Concrete
ℹ️Pile cover is typically higher than an above-ground column's, since the shaft is cast directly against soil or a casing.
Reinforcement
ℹ️Minimum 6 longitudinal bars for a circular pile cage, per common design practice.
ℹ️Commonly 150-200 mm centre-to-centre along the pile shaft.
ℹ️True Helix is geometrically more accurate and gives a leaner estimate. Practical / BBS Convention matches the common site/BBS shorthand (treats each spiral turn like a discrete stirrup) — pick this to reconcile against a hand-prepared BBS.
Lap Splices
ℹ️Commonly 40-50× diameter depending on the applicable code and concrete grade — a deep pile's cage routinely exceeds one 12m stock length.
Cost
For 4 piles at 500 mm diameter × 15.0 m long, you need approximately 12.37 m³ of concrete and 986.1 kg of reinforcement steel.
Concrete (all piles)
Concrete volume: 12.37 m³ (436.8 cft)
Cement: 99.8 bags
Sand: 5.20 m³ (183.5 cft)
Aggregate: 10.39 m³ (367.0 cft)
Steel Reinforcement (all piles)
Longitudinal Main Bars: 32 × 16 mm
Helical / Spiral Ties: 400 × 8 mm
Total steel weight: 986.1 kg
| Bar Type | Diameter | Count / Spacing | Cutting Length | Total Length | Weight |
|---|---|---|---|---|---|
| Longitudinal Main Bars | 16 mm | 32 | 15.540 m | 497.28 m | 785.83 kg |
| Helical / Spiral Ties | 8 mm | 150 mm c/c (400) | 1.267 m | 506.86 m | 200.24 kg |
Assumptions Used
Steel weight: d² ÷ 162 (kg/m) | Helical tie modelled as a true continuous spiral (turn length = √(circumference² + pitch²)), with one combined 20 × diameter anchorage allowance for the whole spiral, not per turn | Concrete dry volume factor: 1.54 | This estimate covers the pile shafts only — it excludes the pile cap (a separate footing-like element) and shuttering (bored/driven piles are cast against the bore hole or a driven casing, not conventional formwork).
Looking for the verification checklist, reference tables, tips, or common mistakes?See the complete Pile Foundation Calculator.
Pile reinforcement schedule with lap splices
This page is set up for pile reinforcement — longitudinal main bars and helical/spiral ties — with lap splices turned on by default, since a deep pile's main bar cage often exceeds a standard 12 m stock bar length.
Edit diameter, count, or pitch and the bar schedule, total weight, and worked example update from the active values — concrete is still calculated in the same result.
- Splices per bar = ROUND UP(effective length ÷ 12 m) − 1, added automatically once the pile exceeds one stock length.
- Tie turns = ROUND UP(pile length ÷ pitch); each turn's length is √(circumference² + pitch²), a true continuous helix, with one combined hook allowance for the whole spiral.
- Minimum 6 main bars enforced for the circular cage, matching common design practice.
How Is the Pile Foundation Quantity Calculated?
The calculation happens in two parts — concrete volume and steel reinforcement (with optional lap splices) — then an optional cost estimate on top, all multiplied across the pile count.
Step 1 — Concrete Volume (per pile, × count)
Pile Volume = π × (Diameter ÷ 2)² × Length
Dry Volume = Wet Volume × 1.54
Cement Bags = Cement Volume ÷ 0.0347 m³/bag (50 kg bags)
Dry volume accounts for the voids between aggregate particles that disappear once the concrete is mixed and compacted. The dry volume is split into cement, sand, and aggregate using the selected mix ratio, and wastage is applied once to the final quantities.
Step 2 — Steel Reinforcement
Effective Length = Pile Length − (2 × Concrete Cover)
Splices per Bar (if laps included) = ROUND UP(Effective Length ÷ 12 m) − 1
Main Bar Cutting Length = Effective Length + (Splices × Lap Multiplier × Diameter)
Tie Circumference = π × (Pile Diameter − 2 × Cover)
Turns per Pile = ROUND UP(Pile Length ÷ Pitch)
Helix Turn Length = √(Tie Circumference² + Pitch²)
Unit Weight (kg/m) = Diameter² ÷ 162
Longitudinal main bars run the full pile length minus end cover; when lap splices are enabled, this calculator estimates how many 12m stock-length splices each bar needs and adds the extra material each splice requires. Helical/spiral ties use the True Helix method: each turn's wire length is the Pythagorean unrolling of the spiral (circumference and pitch as the two legs — always slightly longer than the bare circumference), with one combined hook/anchorage allowance added once for the whole spiral rather than at every turn.
Worked Example
This example walks through your current inputs above, using the same steps as the Formula section.
Input Values Used
| Input | Value | Why it is used |
|---|---|---|
| Pile count | 4 | Multiplies every per-pile quantity to the full group |
| Pile diameter × length | 500mm × 15m | Sets the concrete volume and every bar's base length |
| Mix ratio / wastage | 1:1.5:3, 5% wastage | Converts wet volume to cement bags and adds a buffer for site losses |
| Cover / reinforcement | 50 mm cover, 16 mm main × 8, 8 mm tie @ 150 mm | Sets bar cutting length and tie turn count/size |
| Lap multiplier | 40× diameter | Adds splice length for every 12m stock length exceeded |
Step 1 — Concrete
| Calculation | Substitution | Result |
|---|---|---|
| Wet volume (4 piles) | π × (500mm÷2)² × 15m × 4 | 11.781 m³ |
| With 5% wastage | 11.781 × 1.05 | 12.370 m³ (99.8 bags) |
Step 2 — Steel
| Bar Type | Substitution | Weight |
|---|---|---|
| Longitudinal Main Bars | 32 × 15.540 m × 16²÷162 | 785.83 kg |
| Helical / Spiral Ties | 400 × 1.267 m × 8²÷162 | 200.24 kg |
| Total steel | Sum of all rows | 986.07 kg |
Therefore, 4 piles of 500mm × 15m need approximately 12.37 m³ of concrete and 986.1 kg of steel.
Disclaimer: This calculator provides approximate results for planning and estimation purposes only. Actual requirements may vary based on site conditions, materials, workmanship, and local building regulations. Always consult a qualified engineer, architect, or construction professional before making final decisions.