TryBuildCalcDPM Calculator for Floor Floor DPM roll quantity estimator
Calculate DPM roll quantity for a floor base, including overlap and wastage.
🕒 Last updated: July 30, 2026
Plinth Footprint
ℹ️Internal footprint length to be filled, from the foundation/plinth drawing.
ℹ️Internal footprint width to be filled.
ℹ️Set to more than 1 if several identical rooms/blocks share this same footprint and fill depth.
Fill Layer
ℹ️Height from formation level to the underside of the PCC bed; commonly 150-450 mm for residential plinths.
ℹ️Extra loose volume needed over the compacted volume — pre-filled per material, adjust if your supplier's data differs.
PCC Bed
ℹ️Commonly 50-100 mm for a residential floor base.
DPM (Damp-Proof Membrane)
ℹ️Accounts for the minimum ~150mm lap required at every joint between sheets.
ℹ️Extra allowance for the upturn at edges/walls and offcuts.
Cost
For a 99.00 m² (1,066 sqft) plinth footprint filled 200 mm deep with soil / select fill, you need approximately 41.84 tonnes of fill material and 7.796 m³ (275.3 cft) of PCC bed concrete.
Compacted Fill
Material: Soil / Select Fill
Compacted volume: 19.800 m³ (699.2 cft)
Loose volume (before wastage): 22.770 m³ (804.1 cft)
Loose volume (with wastage): 23.909 m³ (844.3 cft)
Material to order: 41.84 tonnes
PCC Bed (1:4:8)
Thickness: 75 mm
Total concrete: 7.796 m³ (275.32 cft)
Cement: 26.6 bags
Sand: 3.694 m³ (130.5 cft)
Aggregate: 7.388 m³ (260.9 cft)
DPM (Damp-Proof Membrane)
Area with laps/wastage: 108.90 m² (1,172.2 sqft)
Roll coverage: 120.00 m²/roll
Rolls needed: 2
Assumptions Used
Fill: loose volume = compacted volume × (1 + compaction%), then wastage on top | PCC: dry volume factor 1.54, wastage applied to cement/sand/aggregate together | DPM: rolls = ceil(area × (1 + wastage%) ÷ (roll area × (1 − overlap%))) | Flooring/screed/tiling above the DPM is outside this calculator's scope — see Limitations.
Approximate results for planning only. Verify with a professional.
Unsure where the DPM should sit relative to the PCC bed? Plinth Filling Guide →
Plinth Filling Cross-Section
Looking for the verification checklist, reference tables, or tips and mistakes?See the complete Plinth Filling Calculator.
DPM roll requirement estimate
This page has DPM switched on by default to show the roll-count workflow directly: an 11 m x 9 m footprint (99 m²) inflated by the default 10% DPM wastage allowance to 108.9 m² of final area to cover. With the default 30 m x 4 m roll size and a 10% overlap allowance at every joint, each roll's effective coverage drops to 108 m², so it takes 2 rolls to cover the area (ROUND UP(108.9 / 108) = 2).
The fill and PCC bed sections still calculate alongside the DPM using this page's footprint at the calculator's default 200 mm soil fill depth and 75 mm PCC bed — the DPM is the final layer laid over that PCC bed, before the floor slab is poured on top.
- Default footprint: 11 m x 9 m (99 m²), DPM included.
- Roll size 30 m x 4 m, 10% overlap, 10% wastage → 108.9 m² final area.
- Result: 2 rolls needed.
How Is Plinth Filling Calculated?
The calculation happens in three parts — compacted fill, PCC bed, and DPM — then an optional cost estimate on top.
Step 1 — Footprint Area
Area = Length × Width
Total Area = Area × Number of Identical Sections
If sections differ in size: Total Area = Sum of (Length × Width × Count) for every section
The footprint is the internal area to be filled, taken from the foundation/plinth drawing. Number of Identical Sections multiplies the whole result for repeated rooms/blocks of the same size; for rooms of different sizes, switch on "Multiple Different-Sized Sections" and the calculator sums every row's area into one combined total automatically.
Step 2 — Compacted Fill
Compacted Volume = Total Area × Fill Depth
Loose Volume = Compacted Volume × (1 + Compaction %)
Loose Volume (with wastage) = Loose Volume × (1 + Wastage %)
Order Quantity (tonnes) = Loose Volume (with wastage) × Material Density ÷ 1000
Delivered fill material is loose and has more air voids than it will once compacted in place, so the compaction percentage inflates the compacted (finished) volume into the loose volume you actually need to order; wastage is then applied on top of that loose volume, and the resulting figure converts directly to a tonnage using the material's density — the same convention this site's Backfill and Aggregate Coverage calculators use. For "Custom Fill Material", the density you enter is used directly in this step instead of a preset figure.
Step 3 — PCC Bed
Wet Volume = Total Footprint Area × PCC Thickness
Dry Volume = Wet Volume × 1.54
Cement / Sand / Aggregate = Dry Volume split by mix ratio parts
Wastage % applied to cement bags, sand, and aggregate together
This uses the same footprint area as Step 1 (so it stays correct whether you're using a single footprint or several differently-sized sections) and the same PCC formula as this site's dedicated PCC Calculator — a thin, lean-mix concrete bed that gives a firm, level surface for the DPM and floor slab above, not a structural element in its own right.
Step 4 — DPM (Damp-Proof Membrane)
Final Area = Total Area × (1 + Wastage %)
Roll Coverage = Roll Length × Roll Width × (1 − Overlap %)
Rolls Needed = ROUND UP(Final Area ÷ Roll Coverage)
Wastage accounts for the edge upturn and offcuts, while the overlap percentage accounts for the minimum lap required at every joint between adjoining sheets so ground moisture can't find a path through.
Step 5 — Add Contingency (Optional)
Base Cost = Fill Cost + PCC Cost + DPM Cost
Contingency Amount = Base Cost × (Contingency % ÷ 100)
Total Cost = Base Cost + Contingency Amount
Contingency is an optional buffer on top of the combined base cost to cover unexpected variance — supplier rate changes, delivery charges, or material substitution. It defaults to 0%; a commonly used range is 5-15%.
Worked Example
This example walks through your current inputs above, using the same steps as the Formula section. Each table shows the calculation, the values substituted in, and the result it produces.
Input Values Used
| Input | Value | Why it is used |
|---|---|---|
| Plinth footprint | 11 m × 9 m, 1 section(s) | Sets the area every layer's volume is built on |
| Fill material / depth | Soil / Select Fill, 200 mm | Sets fill density and compacted volume |
| Compaction / wastage | 15% compaction, 5% wastage | Converts compacted volume into the loose quantity to order |
| PCC bed | 75 mm, 1:4:8, 5% wastage | Sets PCC wet volume and cement/sand/aggregate split |
| DPM roll | 30 m × 4 m, 10% overlap, 10% wastage | Sets roll coverage area and rolls needed |
Step 1 — Footprint Area
The footprint area is the base every layer above is built on — fill volume, PCC volume, and DPM area all scale directly from it.
| Calculation | Substitution | Result |
|---|---|---|
| Area | 11 m × 9 m | 99.000 m² |
| Total area | 99.00 × 1 | 99.000 m² (1,065.63 sqft) |
Step 2 — Compacted Fill
The compacted volume is what the finished, settled fill will occupy. Compaction inflates that into the loose volume, wastage inflates it once more into the loose volume actually ordered, and that final volume converts directly into a tonnage using the material's density — the same figure the cost step below uses.
| Calculation | Substitution | Result |
|---|---|---|
| Compacted volume | 99.00 m² × 200mm | 19.800 m³ |
| Loose volume | 19.800 m³ × 1.15 | 22.770 m³ |
| Loose volume (with wastage) | 22.770 m³ × 1.05 | 23.909 m³ (844.3 cft) |
| Order quantity | 23.909 m³ × 1750 kg/m³ ÷ 1000 | 41.84 tonnes |
Step 3 — PCC Bed
The PCC bed volume comes from the same total footprint area as Step 1, not the fill's compacted volume — it's a separate, thin layer cast on top of the finished fill.
| Calculation | Substitution | Result |
|---|---|---|
| Wet volume | 99.00 m² × 75mm | 7.425 m³ |
| With 5% wastage | 7.425 × 1.05 | 7.796 m³ (275.3 cft, 26.6 bags) |
Step 4 — DPM
The DPM area is inflated by wastage first (for edge upturn and offcuts), then divided by each roll's effective coverage — the roll area reduced by the overlap needed at every lap joint.
| Calculation | Substitution | Result |
|---|---|---|
| Final area | 99.00 × 1.10 | 108.90 m² |
| Roll coverage | 30m × 4m × 0.90 | 108.00 m² |
| Rolls needed | ROUND UP(108.90 ÷ 108.00) | 2 rolls |
Step 5 — Cost & Contingency
| Calculation | Substitution | Result |
|---|---|---|
| Enable cost estimation above to see fill, PCC, and DPM cost | — | |
Therefore, this 99.0 m² plinth needs approximately 41.84 tonnes of fill material, 7.796 m³ of PCC bed concrete, and 2 rolls of DPM.
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 Plinth Filling Calculator.