Concrete Wall Calculator
Works out the concrete for a poured wall — retaining, basement or garden — with any openings deducted from the face area.
Includes the waste allowance — this is the figure to order.
Share sends a link that reopens these numbers. Copy details pastes the full breakdown as a list.
The formula
volume = (length × height − openings) × thickness × (1 + waste)
A wall is a vertical slab. Openings are subtracted as face area before the thickness is applied, since a door reduces the wall over its full depth.
What to watch out for
Poured walls differ from slabs in ways that affect the order:
- Pour rate limits the height. Formwork has a maximum pressure it can take. Tall walls are poured in lifts, and each lift needs to be planned before the truck arrives.
- A wall pour is unforgiving on timing. Concrete has to stay workable across the whole run, so a retarder is common in hot weather.
- Retaining walls need drainage. Water pressure behind an undrained wall is what pushes them over — a drainage layer and weep holes matter more than extra thickness.
- Openings only help a little. Deducting a 2 m² door from an 8 × 2.4 m wall at 200 mm saves 0.4 m³ — worth entering, not worth agonising over.
Frequently Asked Questions
How thick should a concrete wall be?
150 mm (6 in) for a low garden wall, 200 mm (8 in) for a typical retaining or basement wall, more where the retained height is significant. Anything holding back ground over about 1.2 m should be designed rather than estimated.
How much concrete for an 8 m wall?
An 8 m × 2.4 m wall at 200 mm needs 3.84 m³ before waste — about 4.2 m³ ordered, a comfortable full delivery.
Should I deduct openings?
Yes, if they are significant. Enter the total face area of doors and windows; the calculator removes that area over the full wall thickness.
Can I pour a wall in lifts?
Yes, and tall walls usually are — but each lift needs a planned construction joint, and formwork pressure has to be checked. This is where a wall pour stops being a DIY job.