This tool converts site conditions into a risk score, then selects a standard thickness step. It is intended for preliminary landscaping guidance, not structural certification.
- Risk score = (Use×2) + Load + Soil + Drainage + Material + Size + Climate + Slope
- Thickness is chosen from 40, 50, 60, 70, 80, or 100 mm.
- Base depth increases as loads rise and soils weaken.
- Select your use case and expected loads.
- Choose soil and drainage based on a quick site check.
- Enter your paver size and typical surface slope.
- Enable freeze–thaw if winter cycling is common.
- Review thickness, base depth, and notes.
- Download CSV or PDF to share your plan.
| Scenario | Use | Soil | Drainage | Paver size (mm) | Suggested thickness (mm) | Base depth (mm) |
|---|---|---|---|---|---|---|
| Stepping path | Walkway | Sand | Good | 200 | 40–50 | 100–140 |
| Seating patio | Patio | Loam | Average | 300 | 50–60 | 150–210 |
| Pool deck | Pool deck | Loam | Average | 400 | 60 | 170–230 |
| Family driveway | Driveway | Clay | Average | 200 | 70–80 | 240–320 |
| Service access lane | Service access | Fill | Poor | 600 | 80–100 | 320–450 |
Load categories and typical thickness bands
Paver thickness is commonly grouped into standard bands: 40–50 mm for pedestrian garden paths, 50–60 mm for patios, and 70–80 mm where cars or frequent carts are expected. Heavy service access can require 80–100 mm units, plus stronger edge restraint. This calculator converts your use case and load class into a risk score, then selects the nearest practical thickness step overall.
Soil strength, settlement, and why base depth rises
A stable surface depends more on the compacted base than the paver itself. Gravelly or sandy soils usually need less support, while clay and unknown fill are more prone to movement. The base depth output increases in 10 mm steps and is capped at 450 mm to keep recommendations realistic reliably. When soils are weak, geotextile separation and improved drainage help reduce long‑term settlement.
Drainage and freeze–thaw performance
Poor drainage is a leading cause of heave and joint washout. A 1–2% surface slope typically sheds water without feeling steep, and subgrade shaping should direct water away from structures. If freeze–thaw exposure is enabled, the risk score increases and the calculator pushes toward thicker pavers and deeper bases. In cold climates, preventing trapped water is often more important than adding thickness.
Material and size effects for large-format units
Large-format pavers (over 300 mm on the longest side) can bridge small voids and rock if bedding is inconsistent, so the calculator applies a size penalty above 300 mm and a stronger penalty above 600 mm. Porcelain and natural stone installations typically benefit from tighter tolerances, clean bedding, and robust edge restraint. Permeable systems add depth for open‑graded layers.
Interpreting the confidence score and next steps
The confidence score reflects uncertainty drivers such as poor drainage, weak soil, steep slopes, and freeze–thaw risk. A score above 80 suggests a straightforward garden build, while 55–70 indicates that drainage, compaction quality, and edge restraint deserve extra attention. For driveways and service access, verify local material specs and compaction targets, then test a small area before completing the full surface.
FAQs
1) Is a thicker paver always better?
Not always. Thickness helps under higher loads, but base depth, compaction, and drainage usually control performance. A well-built base with correct slope can outperform thicker pavers on a weak base.
2) What base depth should I use for a typical patio?
Many patios perform well with roughly 150–210 mm of compacted base, depending on soil and drainage. Use the calculator output, then adjust to local aggregate availability and site constraints.
3) How do I choose between jointing sand and polymeric sand?
Jointing sand is flexible and easy to refresh. Polymeric sand resists washout and weeds for light traffic, but it needs dry installation conditions and careful cleanup to prevent haze.
4) What slope should I target for water runoff?
A 1–2% slope is common for garden paving to shed water without discomfort. Steeper grades can increase movement and require stronger restraints and careful bedding control.
5) Do permeable pavers need a different build-up?
Yes. Permeable systems typically use open-graded bedding and base layers, often deeper than standard builds, to store and infiltrate water. Keep fine soils separated with appropriate geotextiles.
6) When should I consult a professional?
Consult a local engineer or experienced contractor for repeated heavy vehicle loads, expansive clays, unknown fill, or persistent drainage issues. Site-specific design can prevent costly failures.