Raised bed load input form
Use one overall stacked page layout. Inside the calculator, the form shifts to three columns on large screens, two on medium screens, and one on mobile.
Load comparison graph
The chart compares dry, moist, saturated, and design cases. It helps you see how moisture and safety margin change the final support demand.
Example data table
These example scenarios show how the calculator can be used for practical garden planning.
| Example | Outer Size | Layer Setup | Saturated Load | Surface Pressure | Design Load |
|---|---|---|---|---|---|
| Compact patio bed | 1.20 × 0.90 × 0.45 m | 0.30 soil + 0.10 drainage + 0.05 mulch | 520.8 kg | 4.73 kPa | 651.0 kg |
| Medium kitchen garden bed | 1.80 × 1.20 × 0.55 m | 0.35 soil + 0.10 drainage + 0.05 mulch | 1156.4 kg | 5.25 kPa | 1445.5 kg |
| Long production bed | 2.40 × 1.20 × 0.60 m | 0.40 soil + 0.10 drainage + 0.05 mulch | 1712.0 kg | 5.83 kPa | 2140.0 kg |
Formula used
- Footprint area = external length × external width
- Internal length = external length − 2 × wall thickness
- Internal width = external width − 2 × wall thickness
- Internal planting area = internal length × internal width
- Soil volume = internal planting area × soil depth
- Drainage volume = internal planting area × drainage depth
- Mulch volume = internal planting area × mulch depth
- Component load = component volume × bulk density
- Total load = soil load + drainage load + mulch load + frame weight + extra fixed load
- Surface pressure = total load ÷ footprint area
- Design load = saturated total load × safety factor
How to use this calculator
- Select the unit you want to use for all dimensions.
- Enter the bed’s external length, width, wall thickness, and total height.
- Enter the soil, drainage, and mulch depths inside the bed.
- Choose a soil preset or type in custom dry, moist, and saturated densities.
- Add frame weight, accessories, and a safety factor for design planning.
- Click calculate to see total weight, support pressure, downloads, and the Plotly graph.
FAQs
1. What does this calculator estimate?
It estimates the filled raised bed weight and the pressure placed on the supporting surface. It includes soil, drainage, mulch, frame weight, and any extra fixed load you choose to add.
2. Why are dry, moist, and saturated results different?
Soil mass changes a lot with water content. Dry values help with transport and setup. Saturated values are more useful for checking the heaviest likely condition after irrigation or rainfall.
3. Why does wall thickness matter?
Wall thickness reduces the internal planting space. That changes the actual fill volume and the final weight. Thicker walls also matter because the external footprint area stays the same while the usable interior shrinks.
4. Should I always trust the saturated load most?
For support checks, yes, it is usually the safer reference. Beds become heavier during storms, after irrigation, or when drainage slows. The design load adds an extra safety margin beyond that condition.
5. Can this prove a deck or balcony is safe?
No. It estimates the load only. The actual capacity depends on joists, spans, connectors, materials, age, and local design rules. Use the results as planning data, then compare them with verified structural capacity.
6. What soil density should I choose?
Use lightweight values for airy bagged raised bed mixes, balanced values for common compost-topsoil blends, and heavy values for mineral-rich soils. Custom inputs are best when you know your material or supplier specification.
7. Why add a safety factor?
A safety factor gives you a more cautious planning value. It helps cover uncertainty in moisture, compaction, material variation, and added accessories. Many gardeners use it when comparing against support limits.
8. Can I use feet or inches instead of meters?
Yes. Choose feet, inches, centimeters, or meters from the unit selector. The calculator converts everything internally and still reports the key outputs in both metric and imperial formats.