GardenKitHow it works
Measure the inside bed dimensions, the desired finished soil depth and the depth already filled. The calculator uses the remaining uniform depth across the entire bed. Add a separate allowance if you want extra material for your own settling estimate, then use the volume printed on the bag. The allowance is not an automatic prediction of compaction. Rocks, irregular bottoms, plant root balls and changing bed shapes are not modeled. Compare the resulting volume with your supplier’s bulk delivery units if buying loose soil.
Formula
Litres = length × width × (target depth − existing depth) × 1000 × (1 + allowance/100). Bags = round up (litres ÷ litres per bag).
Example
A 3 × 1.2 m bed, filled from 5 cm to 30 cm, needs 900 L before allowance. With 10% extra, plan 990 L. At 40 L per bag, buy 25 bags: 1,000 L purchased. At 6 per bag the estimate is 150. If the bed is already at the target depth, the result is zero bags.
Assumptions and limitations
Use product labels and local growing guidance. Defaults are examples. Assumptions use your inputs, not live weather or crop-specific prescriptions. Volume estimates exclude delivery and tax. Bag quantities round up.
Sources and assumptions
University of Minnesota Extension · Garden bed · University of Minnesota Extension · Water
Frequently asked questions
Are my garden measurements uploaded?
No. The tools save your current bed and settings in this browser. Clear this site’s data to remove them.
Does switching units change the result?
No. Dimensions stay in metres internally. Imperial views use feet and inches, cubic feet for bags and US gallons for water.
Are the defaults recommendations for my plants?
No. They are worked examples. Use product labels, crop requirements, soil moisture and local growing guidance.