Choose a bed shape, enter dimensions, and the tool will calculate volumes, purchase allowances, bags, and optional cost estimates.
A sample setup to validate inputs and outputs.
| Shape | Dimensions | Depth | Beds | Allowances | Typical output |
|---|---|---|---|---|---|
| Rectangle | 120 cm × 60 cm | 30 cm | 1 | 5% settlement, 3% waste | ≈ 216 L gross, ≈ 235 L purchase |
| Circle | Diameter 100 cm | 30 cm | 1 | 5% settlement, 3% waste | ≈ 236 L gross, ≈ 257 L purchase |
| Oval | Major 140 cm, Minor 80 cm | 30 cm | 2 | 8% settlement, 5% waste | ≈ 528 L gross, ≈ 599 L purchase |
- Rectangle Area = Length × Width
- Circle Area = π × (Diameter ÷ 2)²
- Oval Area = π × (Major ÷ 2) × (Minor ÷ 2)
- Trapezoid Area = ((Top + Bottom) ÷ 2) × Length
- Volume Volume = Area × Depth
- Purchase Purchase Volume = Total Volume × (1 + Settlement) × (1 + Waste)
- Void water Void Water = Total Volume × Porosity
- Select the bed shape and the dimension units.
- Enter the bed dimensions and media depth.
- Set the number of beds if you have multiples.
- Add settlement and waste allowances for purchasing.
- Optionally enter bag size and price for cost estimates.
- Click Calculate, then download CSV or PDF if needed.
Sizing a media bed with confidence
Media beds work best when volume is planned, not guessed. This calculator converts common garden units into cubic meters, liters, cubic feet, and US gallons. It also supports multiple beds so you can total a full system in one run.
Depth drives volume directly: doubling depth doubles liters required. For many leafy greens, 25–35 cm supports strong root zones while keeping fill manageable. Use the multi-bed count when modules repeat, then export CSV for procurement and use the PDF as an installation checklist. Recheck measurements after framing and before ordering to avoid costly returns later.
Why shape selection matters
Rectangular beds are easy to measure, but round and oval beds are common in tubs and barrels. A small change in diameter increases area quickly because area scales with radius squared. Trapezoid plans help when beds are wider at the top than the base.
Allowances for settlement and waste
Washed media often settles after the first few cycles. Adding a 5% settlement allowance reduces the risk of exposed liners or low planting depth. Waste allowance covers spillage, trimming, and uneven corners. Combined allowances produce a realistic purchase volume, not just the geometric volume.
Porosity and water held in the voids
Porosity estimates how much water occupies gaps between particles. With 35% porosity, a 300 L bed can hold about 105 L of water in void spaces. This matters for pump sizing, flood-and-drain timing, and overall system buffering during hot weather.
Bag counts, cost, and handling
Suppliers sell media by liters or cubic feet, so the calculator converts the purchase volume to bag counts automatically. Enter bag size and price to estimate cost. If bulk density is known, the tool also estimates handling weight, helping you plan lifting, storage, and delivery logistics.
1) What volume should I order: gross or purchase?
Order the purchase volume when buying media. It includes settlement and waste allowances, so you are less likely to run short after rinsing, leveling, and early compaction.
2) How do I choose settlement and waste percentages?
Start with 3–5% settlement for well-washed media and 2–5% waste for normal handling. Increase allowances for deep beds, irregular shapes, or sites where spillage and trimming are expected.
3) Does porosity equal media water absorption?
No. Porosity here represents water in the gaps between particles, not water absorbed into the media itself. It is a practical estimate for flood-and-drain volume and pump cycling.
4) Why does a small diameter change affect volume so much?
Circular and oval areas grow with the square of the radius. Adding a few centimeters to diameter increases area noticeably, which then increases volume because depth multiplies that area.
5) Can I mix different media types in one bed?
Yes, but calculate total volume first, then split the purchase volume by your planned ratio. If two media products have different bag sizes, compute bags for each product separately.
6) How accurate is the bag count?
Bag counts round up to whole bags because partial bags are rarely sold. Actual fill can vary by particle size and moisture, so keep a small contingency if your supplier allows returns.
7) What units should I measure in for best results?
Use the units you can measure reliably with a tape or ruler, then let the calculator convert. Consistent measurements matter more than the unit choice, especially for depth and diameter.