The Imperial Concrete Mix & Moisture Calculator determines the exact amounts of cement, sand, gravel and water needed when field aggregates carry their moisture. It allows builders to enter the mix ratio, water-to-cement ratio, slab dimensions, and the absorption and current moisture content of each aggregate.
The Calculator:
- adds a 54 % bulking allowance to convert finished volume to loose-dry volume
- splits that adjusted volume according to the chosen mix ratio
- converts cement, sand and gravel volumes to weight using typical bulk densities (94 lb/ft³, 100 lb/ft³ and 110 lb/ft³)
- calculates batch water from the w/c ratio and then corrects it by subtracting "free" water already present in the aggregates
- outputs adjusted aggregate weights and the net water to be added in pounds, US gallons and Imperial gallons
Based initially on ACI field-batch guidance introduced in the 1940s, the workflow remains standard practice for ready-mix quality control. Use the results to order materials, fine-tune on-site water, or document compliance tests.
Imperial Concrete Mix & Moisture - Calculation Formulas
$$V = L\,W\,\frac{D}{12}$$
$$V_{\text{dry}} = 1.54\,V$$
$$P = c+s+g$$
$$V_c=\frac{c}{P}V_{\text{dry}},\quad
V_s=\frac{s}{P}V_{\text{dry}},\quad
V_g=\frac{g}{P}V_{\text{dry}}$$
$$M_c = 94\,V_c,\;
M_s = 100\,V_s,\;
M_g = 110\,V_g$$
$$M_w = \left(\frac{w}{c}\right)M_c$$
$$G_{US}=\frac{M_w}{8.34},\;
G_{Imp}=\frac{M_w}{10.022}$$
$$\text{FMC}_{s}= \max(0,m_s-a_s),\;
\text{FMC}_{g}= \max(0,m_g-a_g)$$
$$M_{s\_adj}=M_s+M_s\frac{a_s}{100},\;
M_{g\_adj}=M_g+M_g\frac{a_g}{100}$$
$$M_{\text{free}} = M_s\frac{\text{FMC}_{s}}{100}+M_g\frac{\text{FMC}_{g}}{100}$$
$$M_{w\_adj} = \max(0,M_w-M_{\text{free}})$$
$$M_{\text{total}} = M_c+M_s+M_g+M_w$$
Worked example
Slab 12 ft x 10 ft x 4 in, mix 1 : 2 : 3, w/c 0.60, sand abs 1 %, sand moist 4 %, gravel abs 0.5 %, gravel moist 2 %.
| Item | Result |
|---|
| Finished volume V | 40.0 ft³ |
| Dry volume | 61.6 ft³ |
| Cement weight | 964 lb |
| Sand weight (dry) | 1924 lb |
| Gravel weight (dry) | 2886 lb |
| Batch water | 579 lb (69.4 US gal) |
| Free water in agg. | 90 lb (10.8 US gal) |
| Net water to add | 489 lb (58.6 US gal) |