Buying potting mix sounds easy—until you’re standing in front of a pallet of 50L bags trying to guess how many you need.
Here’s a quick, reliable method to calculate liters for common planter sizes, then convert that into 50L bag counts.
Note: These planter dimensions are most commonly listed in millimeters for retail planters. The calculations below assume: (converted to cm for liters).
- 800 × 360 × 360 mm
- 1000 × 420 × 420 mm
- 1200 × 500 × 500 mm
Quick Rules (Save These)
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Liters needed = (Length × Width × Height in cm) ÷ 1000
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50L bags needed = (Total liters ÷ 50)
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Don’t fill to the absolute brim—assume 5–10% “headspace” for watering.
- Add 10% buffer (spillage, settling, topping up later).
- If you add a drainage layer (e.g., scoria), subtract that volume from soil.
Planter Size Calculations (Liters + 50L Bags)
1) 800 × 360 × 360 (assumed mm)
Converted to cm: 80 × 36 × 36 cm
Volume: 80×36×36 = 103,680 cm³ = 103.7 L
50L bags: 103.7 ÷ 50 = 2.1 bags → Buy 3 bags (includes buffer)
2) 1000 × 420 × 420 (assumed mm)
Converted to cm: 100 × 42 × 42 cm
Volume: 100×42×42 = 176,400 cm³ = 176.4 L
50L bags: 176.4 ÷ 50 = 3.5 bags → Buy 4 bags
3) 1200 × 500 × 500 (assumed mm)
Converted to cm: 120 × 50 × 50 cm
Volume: 120×50×50 = 300,000 cm³ = 300 L
50L bags: 300 ÷ 50 = 6 bags → Buy 6–7 bags (if you want topping-up spare)
How to Get the “Perfect Fill”
Fill to about 2–3 cm below the rim, water once (it settles), then top up. That’s why having one extra bag on larger planters can save a second trip.
Still have questions? Contact us—we’ll help you choose the correct amount of potting mix to pair with our planters.
