🪣 Concrete Mix Design

Written and maintained by the PhDino author · Last reviewed 21 September 2026 · A documented rule of thumb, pinned by automated tests · how PhDino checks its numbers

Related standards: ACI 211.1

Turning a volume of concrete into bags of cement, sand, gravel, and water using a simple proportion mix.

Concrete is really two things combined: cement paste (Portland cement plus water) and aggregate (sand plus gravel or crushed stone) that the paste binds together. The paste does the chemical work of hardening; the aggregate is there mostly to fill volume cheaply and add bulk strength, since aggregate is far less expensive than cement paste itself.

A common DIY approach specifies the mix as a simple volume ratio — for example 1:2:3 (cement:sand:gravel) for general-purpose concrete work — rather than a full lab-verified mix design. That ratio, plus a target water-cement ratio, is enough to estimate quantities for a small pour.

One detail trips people up the first time: the dry, loose ingredients occupy noticeably more volume than the wet concrete they produce. Loose sand and gravel have air gaps between the particles; once mixed with cement paste and placed, those gaps collapse as the paste fills them. A commonly used rule of thumb is that the dry loose volume runs about 1.54 times the finished wet concrete volume — which is why "1 cubic yard of concrete" needs noticeably more than 1 cubic yard of loose dry materials on hand.

Key formula

Dry volume ≈ 1.54 × wet concrete volume
Each component volume = dry volume × (its ratio ÷ sum of ratios)
Mixing water = cement weight × water-cement ratio

Variables

w/c

water-cement ratio by weight — lower gives higher strength but a less workable (harder to place) mix

Notes & limitations

• This is a batching estimate for a volume-ratio mix, not a strength design. Structural work that needs to hit a specific compressive strength (a load-bearing footing, for instance) calls for a proper lab-verified mix design under ACI 211.1, which also accounts for aggregate moisture content and specific gravity that a simple ratio mix ignores.
• A standard 94 lb bag of Portland cement is close enough to 1 cubic foot loose volume that "bags of cement" and "cubic feet of cement" are nearly interchangeable for quick estimating.