Calculate excavation volume, backfill, and concrete fill for trenches. Enter length, width, and depth to get accurate quantities for utilities, footings, and drainage.
Calculate concrete volume from length × width × depth, with slab depth presets
Covers spillage, uneven sub-base, and over-dig
UK building regulations require 150mm working space each side of the footing. So a 600mm footing needs a 900mm trench. For deeper trenches, you may need to widen further for safe access.
Trenches over 1.2m deep must be shored or battered back to prevent collapse. HSE regulations require trench support for any excavation where personnel enter. Always follow HSE guidance on trench safety.
Backfill in 150mm layers, compacting each layer with a vibrating plate. Uncompacted backfill will settle over time, causing problems with paving, floors, or landscaping above. Do not use clay or organic material as backfill.
Sand and gravel are stable and easy to excavate. Clay can be unstable when wet. Chalk is generally stable. Made ground (previously disturbed soil) is unpredictable and may need engineering assessment. Always check soil type before excavation.
V_exc = length × (width + 0.3) × depth
V_conc = length × width × concrete_depth
V_back = V_exc - V_conc
V_muck = V_exc (loose, typically ×1.2 bulking factor)
Trenching is dangerous. Excavations over 1.2m deep require shoring, battering, or trench boxes under HSE regulations. Always check for underground services before excavation (dial before you dig). On unstable ground or near existing structures, consult a groundworks contractor or structural engineer.
Multiply trench length by trench width (including working space) by depth. For a 10m trench at 900mm wide × 1m deep: V = 10 × 0.9 × 1.0 = 9.0 m³. Remember to add 20% bulking factor for muck-away.
For a 10m trench at 600mm wide × 1m deep (full trench fill): V = 10 × 0.6 × 1.0 = 6.0 m³. With 5% waste: 6.3 m³. At £120/m³: about £756.
Typical bulking factors: sand/gravel 1.1-1.2, clay 1.2-1.3, chalk 1.3, mixed soil 1.2-1.25. This means 1m³ of in-situ soil becomes 1.1-1.3m³ when excavated and loose.
Footing width (typically 600mm) plus 150mm working space each side = 900mm minimum. For deeper trenches over 1.5m, widen to 1.2m for safe access. Check HSE and building regulations.