Work out how much soil you need to raise a plinth or backfill around a foundation. Enter the plinth area or room sizes and the filling height, and the calculator gives the soil to bring in cu ft, m³ and brass, with an allowance for compaction, and the number of truck or tractor trips. Part of our quantity surveying tools.
How to use the plinth filling calculator
- Choose Whole plinth, Room by room or Backfill, and feet or metres.
- For a whole plinth, enter the area and the share taken up by walls and columns. For rooms, enter each room’s inner size.
- Enter the filling height, from ground level to the underside of the floor base.
- For backfill, enter the excavation volume and the volumes of the sand bed, PCC, footings and other solid work below ground.
- Choose the compaction allowance and the size of the vehicle.
- Add rates if you want a cost, then download the result as CSV, print it or share a link.
Plinth Filling Calculator
How much soil to bring in for plinth filling or foundation backfill, and how many truck or tractor trips it takes
Labour and rates
Quantity
Checks
Quantity estimate. Actual soil use depends on the soil, its moisture and how it is compacted. Fill material and plinth wall design must follow your drawing or engineer's advice.
Formulas used
| Item | Formula |
|---|---|
| Area to fill | Plinth area − walls and columns, or the sum of room length × width |
| Space to fill | Area to fill × filling height |
| Foundation backfill | Excavation − sand bed − PCC − footings − columns and other solid work |
| Soil to bring | Space to fill × (1 + compaction % ÷ 100) |
| Trips | Soil to bring ÷ vehicle capacity, rounded up |
| Labour by hand | Soil in m³ × 0.6 days per m³ (change it to suit your site) |
| Units | m³ × 35.3147 = cu ft; cu ft ÷ 100 = brass |
Worked example
A plinth of 1200 sq ft filled 2 ft high with ordinary soil:
- Space to fill: 1200 × 2 = 2400 cu ft, or about 68 m³.
- Compaction allowance at 30%: 720 cu ft.
- Soil to bring: 3120 cu ft, or about 88 m³ and 31.2 brass.
- Trips: 3120 ÷ 500 = 6.24, rounded up to 7 truck trips, or 45 tractor trips at 70 cu ft.
- Layers: 2 ft is about 61 cm, so at least 4 layers of no more than 20 cm each.
If walls and columns take up 10% of that plinth, deduct them first: the soil to bring falls to 2808 cu ft.
Frequently asked questions
How do I calculate plinth filling quantity?
Multiply the area to be filled by the filling height, then add an allowance for compaction. For 1375 sq ft filled 4 ft high, the space is 5500 cu ft. Adding 30% for compaction, you need 7150 cu ft of soil.
How much extra soil is needed for compaction?
Site estimates commonly add about 25 to 35%, because loose soil settles when it is watered and rammed. Sandy soil is at the lower end and clayey soil at the higher end. The calculator starts at 30%, which you can change.
How many tractor loads of soil are needed for plinth filling?
Loads = soil needed ÷ capacity of the vehicle, rounded up. For 7150 cu ft of soil, a truck carrying 500 cu ft needs 15 trips and a tractor carrying 70 cu ft needs 103 trips. Check the real capacity with your supplier.
How thick should each layer of plinth filling be?
CPWD specifications call for filling in layers not exceeding 20 cm, with each layer watered and rammed. For a filling 60 cm deep, that means at least three layers.
How do I calculate foundation backfill?
Backfill = excavation volume − sand bed − PCC − footings − columns and any other solid work below ground level. For example, 1800 cu ft of excavation with 350 cu ft of concrete below ground leaves 1450 cu ft to fill.
Should the plinth area include the walls when calculating filling?
No. Filling goes inside the plinth walls. If you enter the outer plinth area, deduct the share taken up by walls and columns, or measure each room’s inner size using the room-by-room option.
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Disclaimer: Online educational publication only. Not a substitute for advice or site supervision by a qualified engineer. Full disclaimer · contact@speakarch.com
Last updated: 9 November 2026