Understanding your result
Volume is the amount to spread. Whole bags round upward; extra litres show what remains after filling the measured area. Costs use your prices without a currency conversion.
Filling a new bed rather than covering its surface? The Raised Bed Soil Calculator splits fill into soil and compost quantities.
The formula
Depth must first be converted to metres. Multiplying square metres by metres gives cubic metres, and each cubic metre contains 1,000 litres. Bulk cost uses the unrounded volume, while bagged cost uses complete bags.
Worked example
A 20 m² bed receiving 5 cm of new mulch needs 1 m³, or 1,000 L. At 50 L per bag, buy 20 bags. Bags priced at 6 cost 120; bulk priced at 95 per m³ costs 95 before delivery.
How to use this calculator
- Measure only the ground that will receive mulch.
- Enter the additional depth, not the combined old and new layers.
- Copy bag volume and supplier prices, then compare the two material totals.
Measure the layer you intend to add
For an irregular border, divide the shape into smaller rectangles and add their areas. Exclude paved sections and areas deliberately left bare around plants. If an existing layer is being topped up, enter only the missing depth; treating the full desired depth as new material can overstate the order.
Compare delivered quotes
The cheaper material subtotal may not be the cheaper purchase. A bulk supplier can charge delivery, set a minimum quantity, or sell in fixed increments. Add those charges when comparing quotes. Bag sizes describe volume, so bag weight is not a substitute unless the supplier provides a density. Loose material can settle after spreading.
Assumptions & limitations
What this calculation assumes
- One uniform additional layer covers the entire entered area.
- Bag volumes are usable volumes as sold.
What to keep in mind
- No compaction, delivery charge, or minimum bulk order is included.
Common questions
Should I enter the existing mulch depth?
No. Enter the thickness of the new material you plan to add after allowing for what remains.
Why does the bag count round up?
A partial final bag is still a whole purchase. The extra-volume result separates that purchase allowance from the amount needed on the ground.