Build stronger benches for potting and repairs. Compare wood or steel tops with safety factors. See load limits instantly, then export a tidy report.
| Scenario | Material | Top size | Span | Safety factor | Uniform capacity (approx.) |
|---|---|---|---|---|---|
| Potting bench in shed | Plywood (Exterior) | 1.5 m × 0.6 m × 38 mm | 1.2 m | 2.0 | ~120 kg |
| Heavy tool station | Hardwood | 1.8 m × 0.7 m × 50 mm | 0.9 m | 2.5 | ~260 kg |
| Metal-frame garden bench | Steel (Mild) | 1.5 m × 0.6 m × 25 mm | 1.0 m | 2.0 | ~600 kg |
The bench top is modeled as a simply supported beam spanning between strong supports. Capacity is limited by bending stress and by deflection, using the stricter result.
This calculator pairs an allowable bending stress with material stiffness to estimate safe loads and expected sag. Wood varies with grade and moisture, so choose conservative values for potting benches and outdoor frames. Steel and aluminum are more predictable, yet connection slip can dominate. Laminations, torsion boxes, and edge aprons increase stiffness by raising the section’s moment of inertia.
Span is the largest unsupported distance between strong supports along the length. Bending moment scales with span squared, while deflection scales with span to the fourth power, so small span reductions matter. Adding a center rail or extra leg line often multiplies capacity without changing the top. If auto span is used, verify it matches your real leg spacing.
Safety factor reduces allowable stress to cover unknowns such as knots, impact loading, and uneven feet. Deflection limits (like L/240 or L/360) control stiffness and user comfort, which is critical when leveling seed trays or using a vise. For shared workshops or heavy garden tool stations, increase safety factor; for precision tasks, tighten the deflection rule.
Uniform load models distributed items like stacked soil bags, trays, or pavers spread across the top. Point load models a concentrated tool or planter near midspan, where bending is highest. Moving a heavy item closer to a leg reduces moment and may improve real capacity. For presses or repeated hammering, treat loads as higher than static weight.
The model assumes a simply supported top; real benches also depend on frame racking resistance. Use diagonal bracing, tight joinery, and solid fasteners to keep supports from spreading. After assembly, apply a gradual test load and measure midspan deflection to confirm it stays within your chosen limit. If sag is high, add blocking, a stretcher, or another support line. Keep the work surface dry when possible, and recheck bolts after an initial week of humid garden use seasonally.
It assumes weight is spread evenly across the span, like bags or trays covering most of the surface. It is not the same as stacking everything in one corner.
It estimates span from bench length and leg count. Use it for early design, then switch to manual span once you know the actual unsupported distance.
A thick top may be strong enough but still feels bouncy. The deflection check limits sag to a chosen ratio so the work surface stays stable.
Yes. Add the top and any built-in shelving weight to your expected loads, especially for long spans. Self-weight reduces remaining capacity.
Reduce span with an extra support line, add an apron, or build a torsion box. Improving bracing against racking also helps supports stay effective.
Only indirectly through the safety factor. Weak joints, loose bolts, or poor bracing can fail first, so build connections stronger than the calculated top capacity.
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.