TryBuildCalcFoundation Backfill Calculator (Structure Deduction, Compaction, Truckloads & Cost)
Calculate backfill volume after structure deduction.
🕒 Last updated: July 30, 2026
Inputs
Choose the source excavation shape. Trench and rectangular use length × width × depth; pit uses top and bottom dimensions.
ℹ️Use this for repeated trenches, pits, or identical excavation bays.
ℹ️If the excavation was actually dug larger than the theoretical dimensions (loose ground, wide bucket, real edges), enter that allowance here so the void size used for backfill matches reality. Carried over automatically from the excavation calculator when linked. Defaults to 0%. Not yet supported for sloped pit excavation.
Structure Deduction
ℹ️Enter footing, wall, pipe envelope, tank, or other built volume inside the excavation.
Select Yes if part of the structure volume is hollow and should not be deducted as solid structure.
Compaction
ℹ️Adds extra loose material to achieve the calculated compacted backfill volume. Typical planning range: 5-15%.
ℹ️Used only to convert volume into an approximate weight in tons — does not affect volume, compaction, or cost.
ℹ️Use the usable volume carried per trip. Typical: 3-10 m³ per trip (about 105-350 cft per trip).
ℹ️Optional buffer for unknowns — supplier density variance, delivery charges, or material substitution. Commonly 5-15%.
Backfill required after structure deduction is 96.000 m³. With compaction allowance, plan for 105.600 m³, requiring 18 truck loads and costing around ₹36,960.
Calculations
Excavation Volume: 144.000 m³ (~230.40 t)
Structure Deduction: 48.000 m³ (~76.80 t)
Net Backfill: 96.000 m³ (~153.60 t)
Compaction Added: +9.60 m³ (~15.36 t)
Adjusted Backfill: 105.600 m³ (~168.96 t)
Estimates
Truck Loads: 18
Estimated Cost: ₹36,960
Approximate results for planning only. Verify with a professional.
Poor compaction and drainage behind a wall are common causes of cracking. Wall Cracks: Causes and Remediation →
Looking for the verification checklist, reference tables, or tips and mistakes?See the complete Backfill Calculator.
Foundation backfill estimate
This page is set up for foundation backfilling where a 10 m x 6 m x 0.8 m concrete footing or wall (48 m³) occupies part of a 12 m x 8 m x 1.5 m excavation (144 m³). Because the excavation footprint is deliberately larger than the footing to allow room for formwork and working space, 96 m³ of net void remains to be backfilled.
With a 10% compaction allowance, the adjusted backfill comes to 105.6 m³, which needs 18 truck loads at 6 m³ capacity per truck, and at 350 per m³ totals roughly 36,960 before any contingency.
- Default excavation: 12 m x 8 m x 1.5 m (144 m³).
- Structure deduction: 10 m x 6 m x 0.8 m footing/wall (48 m³).
- Compaction allowance: 10% → 105.6 m³ adjusted backfill, 18 truck loads.
How does backfill quantity calculation work?
The calculation starts with excavation volume, deducts the solid volume occupied by the structure, then adds a compaction allowance to estimate the loose fill material to arrange.
Step 1 — Calculate Excavation Volume
Pit Volume = Depth ÷ 3 × (Bottom Area + Top Area + √(Bottom Area × Top Area))
If Overbreak is used: Excavation Volume = above × (1 + Overbreak %)
Use rectangular or trench mode for uniform sides. Use pit mode when top dimensions are larger than bottom dimensions due to side slopes. If the source excavation was actually dug larger than its theoretical size, the Overbreak allowance inflates this volume first, so the backfill void calculated below matches the real hole — not just the design dimensions.
Step 2 — Calculate Structure Deduction
Structure Volume = Gross Structure Volume − Void Volume
Void volume is deducted only when Include Voids is set to Yes. This is useful for hollow tanks, ducts, pipes, or other structure volumes that should not be treated as solid displacement.
Step 3 — Calculate Net Backfill
This gives the actual void space to be filled around the completed structure.
Step 4 — Add Compaction Allowance
The adjusted backfill is the loose material volume to order — it is larger than the net void because loose fill needs to be compacted down to fill that void at its final density.
Step 5 — Calculate Truck Loads and Cost
If Truck Capacity is entered in cft: Truck Capacity (m³) = Truck Capacity (cft) ÷ 35.3147
Total Cost = Adjusted Backfill (m³) × Cost per m³
Truck loads are rounded up because fill is normally transported in complete trips. Truck capacity and cost rate can each be entered in m³ or cft — a cft figure is converted to its m³ equivalent first, so the result is identical either way.
Step 6 — Add Contingency (Optional)
Total Cost = Base Cost + Contingency Amount
Contingency is an optional buffer on top of the base cost to cover unexpected variance — supplier density differences, delivery surcharges, or material substitution. It defaults to 0%; a commonly used range is 5-15%.
Example backfill calculation
This example uses the active calculator inputs above and follows the same steps from the formula section — showing the default scenario if you haven't changed anything, or your own live inputs once you do.
Input Values Used
| Input | Value | Why it is used |
|---|---|---|
| Dimensions | 12 m × 8 m × 1.5 m | Sets the rectangular excavation volume |
| Structure deduction | 10 × 6 × 0.8 (m), × 1 | Volume occupied by the structure, subtracted from excavation volume |
| Compaction factor | 10% | Converts net backfill void into loose material to order |
| Equipment & cost | 6 m³/trip, ₹350 per m³ | Sets truck loads and total cost |
Step 1 — Calculate Excavation Volume
| Calculation | Substitution | Result |
|---|---|---|
| Excavation volume | 12 × 8 × 1.5 × 1 | 144.000 m³ |
Step 2 — Calculate Structure Deduction
| Calculation | Substitution | Result |
|---|---|---|
| Gross structure volume | 10 × 6 × 0.8 × 1 | 48.000 m³ |
| Structure volume | Gross | 48.000 m³ |
Step 3 & 4 — Net Backfill and Compaction
| Calculation | Substitution | Result |
|---|---|---|
| Net backfill | 144.000 − 48.000 | 96.000 m³ |
| Adjusted backfill | 96.000 × (1 + 10/100) | 105.600 m³ |
Step 5 & 6 — Truck Loads, Cost & Contingency
| Calculation | Substitution | Result |
|---|---|---|
| Truck loads | 105.600 ÷ 6.00 m³ | 18 trucks |
| Base cost | 105.600 × rate | ₹36,960 |
| Total cost | Base cost | ₹36,960 |
Therefore, this job needs approximately 105.600 m³ of loose backfill material, requiring 18 truck loads and costing around ₹36,960.
This page keeps things focused on the calculation above. For the full construction guide — verification checklist, reference tables, usage steps, tips, common mistakes, and limitations.See the complete Backfill Calculator.