No-Dig Bed Calculator: Calculate Compost for New Beds, Top-Dressing, and Raised Beds

The no-dig method, popularised by Charles Dowding, suppresses weeds, feeds the soil, and builds structure without disturbing the soil ecosystem. Its main material requirement is compost — and getting the quantity right saves both money and wasted trips to the supplier. The No-Dig Bed Calculator takes your bed dimensions and chosen application scenario and returns the volume and weight of compost you need.

Three scenarios are supported. New beds on grass or weedy ground require a deep compost layer of 15 cm to smother existing growth. Annual top-dressing of established beds requires a thinner 5 cm layer applied each season. Raised beds with defined sides require a full fill calculation.

The calculator returns results in both litres and cubic metres, alongside an approximate weight estimate based on typical compost density. It also shows how many standard 50-litre bags or bulk bags you will need, making it straightforward to place a supplier order.

Application depths are based on Charles Dowding's published no-dig recommendations: 15 cm for new bed establishment on grass or weeds, and 5 cm for annual maintenance. Raised bed fill calculations use 100% compost or a compost/topsoil blend depending on user preference. Compost density is assumed at 700 kg/m³ for mature garden compost, which is typical for both homemade and bagged compost.

Enter the length and width of your bed or beds in metres. Select your scenario — new bed, annual top-dress, or raised bed. For raised beds, enter the depth of the bed sides. The calculator will display the total volume in litres and cubic metres, the approximate weight, and the number of 50-litre bags or 800-litre bulk bags required.

If creating multiple beds of different sizes, calculate each separately and add the bag counts together before ordering.