Garden Soil Mix Calculator

What is Mel's Mix?

Mel's Mix is the classic Square Foot Gardening blend: equal parts compost, peat moss or coconut coir, and coarse vermiculite. The three-way split gives you a light, fluffy, water-holding medium that drains well and rarely needs digging. This calculator does the volume math so you know exactly how many cubic feet of each ingredient to buy before you head to the garden center.

How the math works

Your bed volume is length & width & depth. Because depth is entered in inches, we divide by 12 to convert to feet, then multiply by the number of beds. That total is split by the ratio parts you set. Leave all three parts at 1 for a true one-third each Mel's Mix, or nudge them if your compost is rich and you want a little less. Everything updates the moment you type, so you can compare bed sizes instantly.

How to use it

1. Enter your bed length and width in feet, and the fill depth in inches.
2. Set how many identical beds you are filling.
3. Keep the compost, peat/coir, and vermiculite parts at 1 each for the standard blend, or adjust them.
4. Read the cubic feet of each ingredient from the result cards and round up when buying bags.

These figures are planning estimates, not professional horticultural advice; soil settles and bag sizes vary, so buy a little extra.

FAQ

Can I use coconut coir instead of peat?

Yes. Coir is a sustainable, pH-neutral swap for peat moss at the same one-third volume, so use the peat/coir field either way.

How deep should a raised bed be?

Six inches is the traditional Square Foot Gardening depth. Go 10 to 12 inches for root crops like carrots or potatoes.

Why does my mix settle after watering?

Fresh compost and peat compress as they wet down. Overfill slightly or top up after the first few waterings.

How many bags will I need?

Compost and vermiculite are often sold in 2 or 3 cubic foot bags. Divide each result by your bag size and round up.