Soil Calculator - Topsoil & Compost Needed
Calculate exactly how much topsoil, compost, or growing medium you need for your UK garden project. Our calculator provides results in cubic metres, tonnes, and bulk bag quantities, with BS 3882 topsoil density calculations for accurate ordering.
For circular raised beds, pots, or round garden features
Break irregular shapes into rectangles/triangles, calculate their areas, and enter the total here
How to Use the Soil Calculator
Follow these simple steps to calculate how much soil you need:
- Select your soil type - Choose from topsoil, compost, or blended mixes based on your project needs
- Measure your area - Enter the length and width in metres (for irregular shapes, see our guide below)
- Choose your depth - Enter the required depth in centimetres based on what you're planting
- Add settling allowance - All soil settles over time; 10% extra is standard
- Get your results - View requirements in cubic metres, tonnes, and bulk bags
UK Soil Types Explained
Understanding the different types of soil available in the UK will help you choose the right product for your gardening or landscaping project.
BS 3882 Premium Topsoil
- Highest quality screened topsoil
- Tested for contaminants & pH
- Ideal for lawns and fine planting
- Density: 1.2-1.3 tonnes/m³
- Price: £70-120 per bulk bag
General Purpose Topsoil
- Good all-round topsoil
- Suitable for most garden uses
- May contain some stones
- Density: 1.1-1.2 tonnes/m³
- Price: £50-90 per bulk bag
Economy/Screened Topsoil
- Budget-friendly option
- Basic landscaping & filling
- May need amending
- Density: 1.0-1.1 tonnes/m³
- Price: £35-60 per bulk bag
Garden Compost
- Rich in organic matter
- Improves soil structure
- Mix with topsoil (20-30%)
- Density: 0.5-0.7 tonnes/m³
- Price: £45-80 per bulk bag
Peat-Free Compost
- Environmentally sustainable
- Good water retention
- Required for RHS gardens
- Density: 0.3-0.5 tonnes/m³
- UK peat ban from 2024
Raised Bed Mix
- Pre-blended 50:50 or 70:30
- Topsoil + compost mix
- Perfect for vegetables
- Density: 0.8-1.0 tonnes/m³
- Price: £60-100 per bulk bag
Recommended Soil Depths for UK Gardens
Different plants need different soil depths to thrive. Use this guide to determine the correct depth for your project:
| Application | Minimum Depth | Recommended Depth | Notes |
|---|---|---|---|
| New Lawn | 100mm (10cm) | 150mm (15cm) | Use BS 3882 Premium for best results |
| Lawn Repair/Top Dressing | 10mm | 20-25mm | Apply in autumn or spring |
| Flower Beds | 200mm (20cm) | 300mm (30cm) | Mix 70% topsoil, 30% compost |
| Salad Leaves & Herbs | 150mm (15cm) | 200mm (20cm) | Shallow-rooted plants |
| Root Vegetables | 250mm (25cm) | 300mm (30cm) | Carrots, parsnips need loose soil |
| General Vegetables | 200mm (20cm) | 300mm (30cm) | Tomatoes, beans, brassicas |
| Raised Beds | 200mm (20cm) | 300-450mm | Use raised bed mix blend |
| Fruit Bushes | 400mm (40cm) | 500mm (50cm) | Raspberries, currants, blueberries |
| Trees & Large Shrubs | 600mm (60cm) | 900mm (90cm) | Hole 3x root ball width |
| Ground Improvement | 50mm (5cm) | 75-100mm | Rotavate into existing soil |
How We Calculate Soil Requirements
Our calculator uses the following formulae to ensure accurate results:
Volume Calculation
Volume (m³) = Length (m) × Width (m) × Depth (m)
Remember to convert depth from centimetres to metres by dividing by 100.
Weight Calculation
Weight (tonnes) = Volume (m³) × Density (t/m³)
Density varies by soil type and moisture content. Wet soil is heavier.
Bulk Bags Needed
Bulk Bags = Volume (m³) ÷ 0.6 (round up)
A standard bulk bag contains approximately 0.6m³ or 850-1000kg.
Worked Example
Calculate soil needed for a 4m × 3m raised bed at 30cm depth:
Step 1: Calculate area
4m × 3m = 12m²
Step 2: Calculate volume
12m² × 0.30m = 3.6m³
Step 3: Add 10% settling
3.6m³ × 1.10 = 3.96m³ ≈ 4m³
Step 4: Calculate weight (using raised bed mix at 0.9 t/m³)
4m³ × 0.9 = 3.6 tonnes
Step 5: Calculate bulk bags
4m³ ÷ 0.6 = 6.67 → 7 bulk bags needed
Soil Coverage Reference Table
Quick reference for how much area one bulk bag (0.6m³) of topsoil will cover:
| Depth | Coverage per Bulk Bag | Coverage per Tonne | Typical Use |
|---|---|---|---|
| 25mm (1 inch) | 24m² | 20m² | Lawn top dressing |
| 50mm (2 inches) | 12m² | 10m² | Light ground improvement |
| 75mm (3 inches) | 8m² | 6.7m² | Mulching/soil improvement |
| 100mm (4 inches) | 6m² | 5m² | New lawn preparation |
| 150mm (6 inches) | 4m² | 3.3m² | Standard beds/borders |
| 200mm (8 inches) | 3m² | 2.5m² | Vegetable beds |
| 300mm (12 inches) | 2m² | 1.7m² | Raised beds |
UK Topsoil Costs 2024-2025
Typical prices for topsoil and growing media in the UK. Prices vary by region and supplier:
| Product | Bulk Bag Price | Loose Per Tonne | Notes |
|---|---|---|---|
| Economy Screened Topsoil | £35-60 | £30-45 | Basic landscaping |
| General Purpose Topsoil | £50-90 | £40-60 | Most popular choice |
| BS 3882 Premium Topsoil | £70-120 | £55-85 | Quality certified |
| Organic Topsoil | £80-130 | £65-95 | Soil Association approved |
| Garden Compost | £45-80 | £35-55 | Green waste composted |
| Raised Bed Mix | £60-100 | £50-75 | Pre-blended topsoil/compost |
| Peat-Free Compost | £50-90 | N/A | Environmentally friendly |
Cost Example
For a typical raised bed project needing 4m³ of raised bed mix:
- 7 bulk bags at £80 each = £560 + £60 delivery = £620 total
- Loose delivery (4 tonnes at £65/t) = £260 + £50 delivery = £310 total
Loose delivery saves nearly 50% but requires access for a tipper truck.
Where to Buy Topsoil in the UK
UK sources for quality topsoil and growing media:
Builders Merchants
- Jewson, Travis Perkins, Buildbase
- Bulk bags and loose delivery
- Trade accounts available
- BS 3882 certified options
- Collect or delivery
Garden Centres
- Dobbies, Wyevale, independent centres
- Pre-packed 25kg-40kg bags
- Specialist blends available
- Expert advice on-site
- Convenient for small quantities
DIY Stores
- B&Q, Wickes, Homebase
- Bagged soil and compost
- Often on multi-buy offers
- Click & collect available
- Good for small projects
Specialist Suppliers
- Local landscape suppliers
- Best prices for large orders
- Tipper delivery for bulk
- Can mix custom blends
- Often family-run businesses
Online Suppliers
- Compost Direct, Rolawn
- Nationwide delivery
- Compare prices easily
- Customer reviews available
- Good for premium products
Free/Cheap Sources
- Council composting schemes
- Local building sites (ask!)
- Freecycle/Facebook Marketplace
- Own compost heap
- May need screening
Tips for Using Topsoil Successfully
Before Ordering
- Measure accurately - Double-check dimensions before ordering
- Consider access - Can a delivery truck reach your property?
- Check drainage - Poor drainage may need addressing first
- Test existing soil - Know your pH and soil type
- Order 10-15% extra - Account for settling and levelling
During Delivery
- Protect surfaces - Lay boards or tarpaulins for bulk deliveries
- Check quality - Inspect for weeds, stones, and debris
- Position strategically - Place as close to the work area as possible
- Cover if wet weather expected - Wet soil is harder to spread
When Spreading
- Clear the area first - Remove weeds, debris, and old turf
- Break up existing soil - Rotavate or fork to prevent layering
- Don't compact when wet - Avoid walking on wet soil
- Level and rake - Create a fine tilth for planting
- Allow to settle - Wait 2-4 weeks before laying turf
Frequently Asked Questions
For a standard 100mm (10cm) depth of topsoil, you need approximately 0.1 cubic metres per square metre, which equals roughly 120-150kg of topsoil depending on moisture content. For raised beds requiring 300mm depth, you need 0.3 cubic metres or 360-450kg per square metre.
BS 3882 is the British Standard for topsoil quality. It defines three grades: Premium (best for lawns, fine planting), General Purpose (suitable for most landscaping), and Economy (basic ground cover). BS 3882 topsoil is screened, tested for contaminants, and certified for quality. Always request BS 3882 compliant topsoil for important projects.
A standard bulk bag (tonne bag or dumpy bag) contains approximately 0.6 cubic metres and weighs around 850-1000kg. To calculate bags needed: divide your total cubic metres by 0.6 and round up. For example, a 10m² area at 150mm depth needs 1.5m³, which equals 2.5 bulk bags (round up to 3 bags).
Recommended depths: Salad leaves and herbs need 150-200mm, root vegetables like carrots need 300mm, most vegetables and flowers need 200-300mm, fruit bushes need 400-500mm, and trees need 600mm minimum. For raised beds, use a 70/30 mix of topsoil to compost for best results.
UK topsoil prices in 2024-2025: Bulk bags (850-1000kg) cost £50-90 for general purpose or £70-120 for BS 3882 premium. Loose delivery costs £35-60 per tonne plus delivery (typically £30-80). Bagged topsoil (25kg bags) costs £3-6 each, which is more expensive per tonne but convenient for small quantities.
Use topsoil as your main growing medium for structure and drainage - it forms the bulk of beds and lawns. Add compost (20-30% by volume) to improve fertility, organic matter, and water retention. For raised beds, use a mix of 70% topsoil and 30% compost. Never use pure compost for planting as it lacks structure and can become waterlogged.
For irregular shapes, break the area into rectangles, triangles, or circles and calculate each separately. For triangles: (base × height ÷ 2) × depth. For circles: π × radius² × depth. Add 10-15% extra for settling and levelling. Many UK suppliers offer free site visits for large landscaping projects.
Topsoil is the dark, nutrient-rich upper layer (usually 150-300mm deep) containing organic matter, microorganisms, and nutrients essential for plant growth. Subsoil is the lighter layer below, lacking organic matter and nutrients. Never use subsoil for planting - it won't support healthy plant growth. Subsoil is only suitable for filling or raising ground levels before adding topsoil on top.
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Pro Tips for Accurate Results
- Double-check your input values before calculating
- Use the correct unit format (metric or imperial)
- For complex calculations, break them into smaller steps
- Bookmark this page for quick future access
Understanding Your Results
Our Soil Calculator provides:
- Instant calculations - Results appear immediately
- Accurate formulas - Based on official UK standards
- Clear explanations - Understand how results are derived
- 2025/26 updated - Using current rates and regulations
Common Questions
Is this calculator free?
Yes, all our calculators are 100% free to use with no registration required.
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Our calculators use verified formulas and are regularly updated for accuracy.
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