Concrete Basement
Volume Calculator
Calculate the exact volume of concrete needed for your basement floor, walls, footings and columns — with instant cost estimates and bag counts. Completely free.
Basement Dimensions
Enter dimensions for each component you need. Switch between sections using the tabs below.
Enter your basement dimensions and hit Calculate to see your concrete volume and cost estimate.
Concrete volumes by element
| Grade | Strength (N/mm²) | Typical Use | Basement Suitability | Notes |
|---|---|---|---|---|
| C20 | 20 N/mm² | Paths, blinding, light domestic slabs | Not recommended | Too weak for structural basements |
| C25 | 25 N/mm² | Residential floors, house foundations | Adequate | Minimum for most residential basements |
| C30 | 30 N/mm² | Commercial slabs, garage floors | Good | Suitable for basement floors & walls |
| C35 | 35 N/mm² | Waterproof concrete, RC walls | Excellent | Preferred for waterproof tanked basements |
| C40 | 40 N/mm² | High-load structural elements | Specialist | Heavy commercial & industrial only |
For most UK residential basements, C25 or C30 ready-mix is specified. If the basement is waterproofed by the concrete itself (no separate tanking), C35 with a w/c ratio of 0.45 or less is typically required by a structural engineer.
| Concrete Grade | South East UK | Midlands / North | Scotland / Wales | Min. Order |
|---|---|---|---|---|
| C20 | £95 – £115/m³ | £80 – £100/m³ | £85 – £105/m³ | 3–4 m³ typically |
| C25 | £105 – £125/m³ | £90 – £110/m³ | £90 – £115/m³ | 3–4 m³ typically |
| C30 | £115 – £140/m³ | £100 – £120/m³ | £100 – £125/m³ | 3–4 m³ typically |
| C35 | £125 – £155/m³ | £110 – £135/m³ | £110 – £138/m³ | 4–6 m³ typically |
| C40 | £140 – £175/m³ | £120 – £150/m³ | £120 – £155/m³ | 6+ m³ typically |
Prices shown are indicative 2025 UK ranges and exclude pump hire (approx. £400–£800/day), reinforcement, formwork and labour. Prices vary by supplier, season and fuel surcharges. Always obtain at least 3 quotes.
| Bag Size | Volume per Bag | Bags per m³ | Approx. Cost/Bag | Effective Cost/m³ |
|---|---|---|---|---|
| 20 kg bag | ~0.009 m³ | ~108 bags | £5 – £7 | £540 – £756/m³ |
| 25 kg bag | ~0.012 m³ | ~84 bags | £6 – £9 | £504 – £756/m³ |
| 40 kg bag | ~0.018 m³ | ~56 bags | £8 – £12 | £448 – £672/m³ |
| Bulk bag (1 tonne) | ~0.42 m³ | ~2.4 bags | £90 – £160 | £215 – £381/m³ |
Bagged concrete costs 3–6× more per m³ than ready-mix and is only practical for very small pours (under 0.5 m³). For any basement element, ready-mix is almost always more economical and produces a better, more uniform result.
Tips for a successful basement pour
Get a Structural Engineer
Basement concrete must be specified by a structural engineer. They will determine the correct grade, reinforcement layout, cover depths and waterproofing strategy. Never use generic specifications for a basement.
Plan Your Ready-Mix Delivery
Ready-mix trucks hold 6–8 m³. Ensure site access is clear and the pump (if used) is positioned before the truck arrives. Concrete has a short workable life — typically 90–120 minutes — so have your team ready.
Waterproofing is Critical
Basements are below ground — water ingress is a serious risk. The three main approaches are tanked waterproofing (membranes), integral waterproofing (additives in the concrete mix) and drained cavity systems. Your engineer will advise.
Always Add Waste
Always order at least 10% more concrete than your calculated volume. Ground is rarely perfectly level, formwork can flex, and running short mid-pour is very costly. You cannot easily top-up with a second load.
Mind the Weather
Do not pour concrete if the temperature is below 3°C or above 30°C. Cold slows curing (and can cause freeze damage); extreme heat accelerates setting, reducing workability. Use admixtures to adjust if necessary.
Frequently asked questions
Multiply the floor length × width × slab thickness to get the volume in m³. A typical residential basement floor (e.g. 8m × 6m × 150mm thick) requires approximately 7.2 m³ of concrete before waste allowance. Add 10–15% for waste and overpour, giving you roughly 7.9–8.3 m³ to order. Use our calculator above for exact figures.
For most UK residential basements, C25 is the minimum grade and C30 is recommended for floors and walls. If the basement is designed to be waterproof through the concrete itself (no additional tanking), C35 with a water-cement ratio of 0.45 or below is usually required. Your structural engineer will specify the exact grade and mix design. Never guess the grade for a structural basement element.
In 2025, ready-mix concrete in the UK typically costs £90–£175 per m³ depending on grade, region and supplier. C25 ranges from around £90–£125/m³. Note that most suppliers have a minimum order of 3–6 m³, and you’ll also need to budget for concrete pump hire (£400–£800/day), reinforcement, formwork, labour and finishing. Always get at least three quotes.
A typical domestic basement floor slab is 150mm thick minimum, often 200mm for heavily loaded areas or where reinforcement is required. The exact thickness depends on the anticipated loading, ground conditions and your structural engineer’s specification. Thinner slabs (100mm) are sometimes used for lightly loaded scenarios, but this must be engineer-confirmed. Our calculator accepts any thickness you enter.
Technically yes, but it is very rarely practical or cost-effective. Bagged concrete costs 3–6 times more per m³ than ready-mix, and mixing bags consistently for a structural pour is extremely difficult. Even a small basement floor of 5 m³ would require roughly 420 × 25 kg bags, all mixed on-site. For any basement element, ready-mix concrete is the industry-standard approach.
Theoretical volume calculations assume perfectly level ground, perfectly rigid formwork and zero spillage — none of which exist in practice. Ground surfaces are uneven, formwork flexes under pressure, and some concrete is always lost to spillage and residue in chutes and pumps. A 10% waste allowance is standard; use 15% for complex shapes, uneven ground or if it’s your first pour. Ordering too little and needing a second truck is costly and can compromise the structural integrity of the slab.