Calculator
Example data table
| Scenario | Weight | CG height | Base width | Area | Wind | Slope | Typical SF | Interpretation |
|---|---|---|---|---|---|---|---|---|
| Small planter, sheltered | 20 kg | 0.45 m | 0.45 m | 0.25 m² | 6 m/s | 0° | ~1.8 | Low |
| Tall trellis, gusty patio | 18 kg | 1.00 m | 0.35 m | 0.60 m² | 10 m/s | 0° | ~1.0 | High |
| Cart on gentle slope | 35 kg | 0.70 m | 0.50 m | 0.40 m² | 8 m/s | 8° | ~1.2 | Moderate |
| Light frame, open yard | 12 kg | 0.90 m | 0.40 m | 0.90 m² | 12 m/s | 0° | ~0.7 | Critical |
Formula used
This calculator estimates stability by comparing moments about a tipping edge.
- Fwind = 0.5 × ρ × Cd × A × v²
- Mover = Fwind × h + (W × g × h × sin(θ))
- Mres = W × g × (b/2) × cos(θ)
- SF = Mres / Mover
ρ is air density, Cd is drag coefficient, A is exposed area, v is effective wind speed, h is CG height, b is base width, W is total mass, g is gravity, and θ is slope angle.
How to use this calculator
- Select your preferred unit set.
- Enter the empty object weight and any ballast you add.
- Estimate CG height and base width in the tipping direction.
- Measure the projected area facing the wind.
- Enter site wind speed and choose a gust factor if needed.
- Add slope angle if the object sits on sloped ground.
- Click Calculate to see risk and the safety factor.
- Use the ballast suggestion or widen the base to improve SF.
- Download CSV/PDF to save a stability record.
Professional notes
Why tip-over risk matters in gardens
Tip-overs damage plants, crack pots, and injure bystanders. Wind accelerates failures because force rises with the square of speed. A small increase in gusts can double the overturning moment. Quantifying stability helps you decide whether ballast, relocation, or anchoring is needed before storms arrive.
Key inputs that drive stability
The strongest drivers are center-of-gravity height, base width, and exposed area. Tall trellises increase lever arm length, while narrow bases reduce the resisting moment. Use realistic projected area, not surface area, and include anything that catches wind such as foliage, panels, or fabric covers.
Interpreting the safety factor
The safety factor compares resisting moment to overturning moment. Values above 1.50 typically indicate a comfortable margin for everyday outdoor use. Values near 1.00 mean a tip is likely under the chosen gust factor. Values below 0.90 deserve immediate action, especially on hard surfaces.
Ways to reduce risk quickly
Lower the center of gravity by moving heavy items down, or by filling the bottom of a container with stone. Increase base width using outriggers, wider stands, or spacing legs farther apart. Reduce wind load by adding vents, turning the narrow side into the wind, or placing a windbreak upwind.
Using results for maintenance planning
Record a baseline for each movable item and recheck after modifications. Seasonal changes matter: leafy growth increases projected area and can raise drag coefficient. After watering, mass rises and stability improves, but wheels or slick pads lower friction. Pair this result with a routine inspection schedule. For wheeled carts, lock casters and orient wheels across slopes. If anchoring is possible, use ground stakes or wall ties and reduce the assumed base width to the contact points. When you change the gust factor, document the weather source you used so comparisons remain consistent. For public areas, aim for SF 2.0 or higher. Recalculate whenever you add umbrellas, signage, or seasonal shade cloth. Store exports with photos to track geometry changes over time.
FAQs
1) What safety factor should I target?
For home gardens, SF 1.50 is a practical minimum. Use SF 2.00 for public paths, balconies, or windy corners. If the item is tall and lightweight, combine ballast with a wider base.
2) How do I estimate exposed wind area?
Use the projected outline facing the wind. Include foliage, panels, shade cloth, and any flat accessories. For irregular shapes, measure height and width and multiply, then reduce slightly for gaps.
3) Does adding water always improve stability?
Usually yes, because mass increases and the center of gravity may drop. However, water can raise height in tall containers and can slosh. Place ballast low and secure containers to prevent movement.
4) How should I choose a gust factor?
Use 1.0 for steady sites. Use 1.2–1.6 for open yards or turbulent areas near buildings. If you rely on storm forecasts, use a higher factor to represent short gust peaks.
5) Why does slope increase tip-over risk?
On a slope, part of the weight acts downhill and adds overturning moment. The resisting moment also reduces because the effective lever arm shrinks. Leveling pads and orienting bases across the slope helps.
6) What if the ballast recommendation is unavailable?
Very steep slopes or tall items can make ballast alone insufficient. In those cases, widen the base, lower the height, add anchors, or move the item to a sheltered position before windy conditions.