Calculator
Formula Used
This tool computes plan area first, then multiplies by depth:
- Rectangular: Area = L × W
- Circular: Area = π × (D/2)²
- Triangular: Area = ½ × Base × Height
- Trapezoidal: Area = ((A + B) / 2) × Height
- Custom area: Area = user provided
Volume: V = Area × Depth. Then the calculator applies adjustments: Vfinal = V × Beds × (1 + Waste%) × (1 + Settling%).
How to Use This Calculator
- Select the bed shape that matches your plan.
- Choose a unit system and enter the required dimensions.
- Enter depth as the finished soil depth inside the bed.
- Set the number of identical beds to scale the order.
- Add waste and settling percentages for realistic purchasing.
- Enter soil density to estimate weight for delivery planning.
- Set bag size to estimate how many bags to buy.
- Press Calculate to view results and download files.
Example Data Table
| Shape | Dimensions | Depth | Beds | Waste | Settling | Adjusted Volume | 40 L Bags |
|---|---|---|---|---|---|---|---|
| Rectangular | 2.4 m × 1.2 m | 0.30 m | 2 | 5% | 10% | ~1.90 m³ | ~48 |
| Circular | Diameter 1.5 m | 0.25 m | 1 | 5% | 10% | ~0.49 m³ | ~13 |
| Custom Area | Area 30 ft² | 8 in | 1 | 7% | 12% | ~0.72 m³ | ~18 |
Examples are approximate and depend on the adjustment settings.
Professional Guide to Garden Bed Volume Planning
1) Why volume accuracy matters on site
Raised beds behave like small retaining structures: once framed, the internal void defines your material order. Underbuying delays work, while overbuying adds disposal cost. Even a 0.10 m depth error on a 2.4 m × 1.2 m bed changes volume by 0.288 m³ (288 L), roughly seven 40 L bags.
2) Depth selection by crop and build-up
Common finished depths range from 0.20–0.45 m. Leafy greens often perform well around 0.20–0.30 m, while many root crops benefit from 0.30–0.45 m. If you will top-dress annually, plan for settling so the long-term depth remains within your target band.
3) Shape options for real layouts
Construction drawings rarely stay perfectly rectangular. Circular beds suit feature plantings, triangles fit corners, and trapezoids follow property lines. This calculator converts each plan shape into area, then multiplies by depth. For irregular footprints, measure area directly and use the custom-area mode.
4) Waste and settling allowances
Waste accounts for spillage, uneven grading, and minor overfill; 3–8% is typical for hand placement. Settling reflects consolidation after watering and time; 8–15% is common for loose mixes. Combining both can raise your order by roughly 11–24%, improving first-pass completeness.
5) Unit conversion that avoids ordering mistakes
Suppliers may quote cubic meters, cubic yards, liters, or cubic feet. A practical reference: 1 m³ equals 1,000 L, about 35.315 ft³, and about 1.308 yd³. Converting to the supplier’s unit before purchase reduces rounding error and miscommunication.
6) Bag count versus bulk delivery
Bagging helps on tight sites, but labor can dominate. For example, 1.90 m³ is about 1,900 L, which is roughly 48 bags at 40 L each. Bulk delivery becomes efficient when volumes exceed about 1–2 m³, especially if access allows a direct dump near beds.
7) Weight and handling considerations
Density varies with moisture and blend. Loose topsoil commonly falls near 1,000–1,300 kg/m³. At 1,200 kg/m³, a 0.75 m³ order weighs about 900 kg. Use the mass estimate to plan wheelbarrows, staging, and safe manual handling limits.
8) Practical field checklist for consistent results
Measure inside the finished frame, not outside. Confirm depth is the filled soil depth, not timber height. Apply waste and settling intentionally, then round up to supplier increments. Record your inputs and export CSV or PDF for purchasing, inspection notes, and repeat builds.
FAQs
1) What depth should I use for a raised bed?
Most projects use 0.20–0.45 m finished depth. Choose shallower depths for greens and deeper depths for root crops. Include settling so the post-watering depth still meets your target.
2) Should I measure the outside or inside dimensions?
Use inside dimensions because soil fills the internal void. Measuring outside can overestimate volume, especially with thick timber or block walls.
3) What waste and settling percentages are realistic?
Waste is often 3–8% for small jobs. Settling commonly runs 8–15% for loose mixes. If you compact intentionally, reduce settling to match your field method.
4) How do I estimate bags accurately?
Convert the final volume to liters, then divide by bag liters and round up. A 40 L bag is 0.04 m³. The calculator does this automatically and rounds to whole bags.
5) Why does soil density matter?
Density converts volume to weight for delivery and handling plans. Moist, heavy soil can exceed 1,300 kg/m³, while lighter mixes may be closer to 900–1,100 kg/m³.
6) Can I use custom area for irregular beds?
Yes. Measure plan area from a drawing, grid method, or site survey, then enter it with depth. This approach is ideal for curves and composite shapes.
7) How much should I round up for supplier increments?
Round up to the nearest supplier increment, commonly 0.25–0.50 m³ or 0.25 yd³. Keep the CSV/PDF for ordering, and document any on-site adjustments for future repeats.
Measure carefully, then fill beds with confidence and accuracy.