Effective W/C Ratio Calculator

For nominal mix concrete with rain-saturated sand & coarse aggregate

1. Mix Ratio (Cement : Sand : Coarse Aggregate)

Cement ratio part

e.g. 1 in a 1:1.25:2.5 mix

Sand ratio part

Fine aggregate portion

Coarse aggregate ratio part

Coarse aggregate portion

2. Design Water-Cement Ratio

Design (target) w/c ratio

Used to compute design mixing water = w/c × cement weight

Batch volume (m³)

Wet (compacted) concrete volume for this calculation

w/c ratio	0.30	0.35	0.40	0.45	0.50	0.55
Typical grade	M50+	M40-M45	M35-M40	M30	M25	M20

3. Sand Moisture (Site Measured, Rain-Affected)

Measured sand moisture content, MC (%)

From oven-dry test or moisture meter on rain-soaked stockpile; saturated sand typically 5-8%

Sand absorption capacity (%)

Water locked inside particles, does not dilute paste; typical river/local sand: 1-2%

4. Coarse Aggregate Moisture (Site Measured, Rain-Affected)

Coarse aggregate moisture (%)

CA holds less surface water than sand due to lower surface area; rain-wet CA typically 1-3%

Coarse aggregate absorption (%)

Typical for 20mm crushed stone/gravel: 0.5-1%

Output 1: Corrected Water to Add (maintains target w/c ratio)

Water to add at mixer

Water to add per 50 kg cement bag

Resulting w/c ratio (should equal design target)

Output 2: If Full Design Water Is Added Anyway (no correction)

Actual w/c ratio achieved (unintended increase)

Excess water beyond target (litres)

Assumptions Used

Parameter	Assumed Value
Dry volume factor (bulking + voids)	1.54 × wet volume
Cement bulk density	1440 kg/m³
Sand bulk density (dry)	1600 kg/m³
Coarse aggregate bulk density (dry)	1500 kg/m³
Cement bag size	50 kg