Calculator inputs
Example data table
| # | Unit system | Length | Width | Avg lift | Expansion | Waste | Irregularity |
|---|---|---|---|---|---|---|---|
| 1 | Metric | 6.0 m | 3.5 m | 20 mm | 20x | 10% | 1.10 |
| 2 | Metric | 4.2 m | 2.0 m | 35 mm | 18x | 12% | 1.20 |
| 3 | Imperial | 18 ft | 10 ft | 1.5 in | 25x | 8% | 1.15 |
Formula used
The calculator estimates the expanded void volume under the slab, then converts that to required liquid foam using the selected expansion factor and a waste allowance.
- Area = length × width
- Raw void volume = area × average lift height
- Adjusted void volume = raw void volume × irregularity factor
- Liquid foam volume = (adjusted void volume ÷ expansion factor) × (1 + waste%)
- Board feet = adjusted void volume (ft³) × 12
Expansion factor reflects how much the mixed foam grows after injection. Irregularity factor accounts for uneven voids, soil loss pockets, and routing inefficiencies.
How to use this calculator
- Select your unit system before entering measurements.
- Measure slab length and width along the lifted section.
- Estimate average lift height from multiple lift points.
- Choose a realistic expansion factor from product guidance.
- Set waste percent for drill loss and trimming allowance.
- Use irregularity factor when void depth varies under slab.
- Optionally add kit yields to estimate kit quantities.
- Press Calculate, then export results as CSV or PDF.
Measurement and scope definition
Project planning starts with measuring the lifted area and the target elevation change. Using an average lift height avoids overestimating localized high points. When slabs are segmented, calculate each panel separately and add totals. Include only the portion expected to move, not adjacent stable concrete. These inputs drive a realistic void estimate and reduce surprises during injection. Document measurements on site to support scope and billing.
Expansion behavior and liquid demand
Foam products expand differently based on chemistry and temperature. Select an expansion factor from supplier data, then choose the conservative end. Cold substrates and wet soils can lower effective expansion and slow reaction. For sensitive slabs, smaller injections reduce heave and allow gradual leveling. The calculator converts expanded void volume into liquid demand using the factor, then adds a waste allowance for mixing and cleanup losses.
Irregular cavities and staged lifting
Subgrade erosion, pumping, and utility trenches create irregular cavities under concrete. An irregularity factor increases the calculated void volume to reflect these conditions. Use 1.00 for uniform contact, 1.10–1.30 for moderate loss, and higher values only with evidence. Pair the estimate with a thoughtful hole layout and staged lifts. If grout ports reveal rapid take-up, pause and reassess before continuing operations.
Procurement, units, and kit sizing
Procurement is easier when volumes are expressed in multiple units. The tool reports liters and gallons of liquid foam, plus board feet of expanded output. Board feet align with many packaged kit labels and help compare brands. If your kit lists a liquid yield instead, enter that value to estimate kit counts. Round up for mobilization days and keep a contingency for unexpected voids and rework.
Verification, documentation, and closeout
Quality control focuses on lift tolerance, crack response, and final drainage. Verify elevations with a laser or straightedge after each lift stage. Do not chase perfection; stop when movement stabilizes and joints behave normally. Exporting results to CSV supports estimating, job costing, and crew briefings. PDF summaries are useful for submittals and closeout records. Always confirm underground utilities and follow local safety procedures before any drilling.
FAQs
It outputs adjusted void volume, required liquid foam, and expanded foam in board feet. It also shows optional kit counts when you enter kit yield values, plus CSV and PDF exports.
Use the average lift needed across the slab section. Measure several points, ignore isolated peaks, and average the values. For stepped panels, calculate each panel separately and sum results.
Use the value from your foam supplier, then choose conservatively. Cooler temperatures and damp soils can reduce effective expansion. If unsure, increase waste percent rather than inflating expansion.
It increases the void estimate for uneven cavities and soil loss. Use 1.00 for uniform support, 1.10–1.30 for moderate voiding, and higher only when inspections or probing confirm significant loss.
Waste covers mixing losses, hose purge, drill hole leakage, trimming, and minor overfill. Tight access or many small injections often raise waste. Start with 8–15% and adjust based on site experience.
No. Foam take-up depends on subgrade condition, moisture, temperature, and injection strategy. Use the result for planning and purchasing, then track actual usage during lifting to refine future inputs.