Design a floating deck layout in minutes. Choose spacing, overhang, and waste for real sites. Download results as CSV or PDF for crews easily.
| Deck size | Spacing | Overhang | Waste | Recommended blocks |
|---|---|---|---|---|
| 16 ft × 12 ft | 4 ft × 4 ft | 0.5 ft | 7% | 20 |
| 20 ft × 14 ft | 5 ft × 4 ft | 0.5 ft | 10% | 24 |
| 6 m × 4 m | 1.5 m × 1.5 m | 0.15 m | 5% | 16 |
Examples are for planning. Confirm framing, soil, and local requirements.
1) Effective supported span
Effective length = Deck length − 2 × Overhang
Effective width = Deck width − 2 × Overhang
2) Grid points (support locations)
Blocks along length = ceil(Effective length ÷ Spacing length) + 1
Blocks along width = ceil(Effective width ÷ Spacing width) + 1
Base blocks = (Blocks along length) × (Blocks along width)
3) Waste allowance
Recommended blocks = ceil(Base blocks × (1 + Waste% ÷ 100))
4) Simple load check (planning only)
Tributary area per block ≈ Spacing length × Spacing width
Load per block ≈ Tributary area × Design load
Compare load per block to entered block capacity.
Start with finished deck length and width, measured to the outside of decking. Use the same unit system across all fields. Typical backyard platforms are 3.5–6.0 m wide or 12–20 ft wide. Record any constraints like fences, trees, or step landings, because they can change spacing and waste.
The calculator treats blocks as a rectangular grid of support points. After subtracting edge overhang, it divides the remaining span by your chosen spacing and rounds up, then adds one support line to catch the far edge. This produces blocks along length and width, and the base block count is the product of both.
Aim for spacing that matches joist layout, often 1.2 m or 4 ft, so beams land on blocks without shims. On sloped soil, expect more time for leveling and consider a compacted gravel pad under each block for drainage. When your layout includes steps or a heavy grill area, treat that zone as a higher load and tighten spacing locally slightly.
Overhang is the planned cantilever of framing beyond the outermost blocks. A small value reduces the supported span and can lower the total count, but excessive overhang can increase bounce and fastener fatigue. Keep overhang consistent on all sides when possible, and verify that rim and joist sizing matches your span and load.
Waste covers spare blocks, replacement for cracked units, and adjustments during leveling. For simple rectangles, 5–8% is usually adequate; for angled edges or tight access, 10–15% is safer. Stage blocks near corners first, snap layout lines, and confirm diagonals are equal before final leveling.
The load check is a quick planning screen, not a structural certification. It estimates block load from tributary area (spacing × spacing) multiplied by the design surface load you enter. If the estimated load exceeds your stated block capacity, reduce spacing, add intermediate supports, or consult local requirements for occupancy and snow.
Start with a square grid that matches your framing rhythm, commonly 4 ft (about 1.2 m). Then adjust if you have long spans, heavy furniture, or soft ground.
Overhang shortens the supported span used in the grid calculation. With less span to support, fewer support lines may be needed. Keep overhang modest to avoid excessive deflection.
No. Treat steps and landings as separate supported structures. Add dedicated supports under stringers and landings, or reduce spacing in that zone to carry concentrated loads.
Use 5–8% for simple rectangles on easy access sites. Use 10–15% for complex edges, tight delivery paths, or when you expect extra leveling adjustments and spares.
No. It is a planning check only. For compliance, confirm soil conditions, local live-load requirements, and manufacturer capacity limits, and consult a qualified professional when needed.
Expect more leveling time. Prepare stable bearing surfaces under each block, keep drainage moving away, and recheck level after settling. On steeper slopes, consider additional supports or other foundations.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.