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Hydrometallurgy

Filter Cake Moisture & Solids Calculator

Filter-cake moisture is the water held in a discharged filter cake, and it is reported on two different bases that are easy to confuse. From a wet cake mass and a dry (bone-dry solids) cake mass, this calculator returns the wet-basis moisture (water ÷ wet cake), the cake percent solids (the complement of wet-basis moisture), the dry-basis moisture (water ÷ dry solids), the water-to-solids ratio, and the water mass held in the cake. The wet basis and dry basis differ — an 18% wet-basis moisture is a 21.95% dry-basis moisture for the same cake — and stating which basis you mean is the single most common source of error in cake-moisture reporting. It is a preliminary, formula-based, educational mass split of a MEASURED cake. It does NOT predict the moisture a filter will achieve, model dewatering kinetics, or account for bound/hygroscopic moisture beyond the measured wet/dry split, and it does NOT design or select a filter. The cake moisture is a property of the cake you measured, not a predicted value.

TypeInteractive engineering calculator

Calculator

kg

as-discharged wet filter cake

kg

bone-dry solids (oven-dried to constant mass)

Result
Moisture (wet basis)18 %
Moisture (dry basis)21.9512 %
Cake solids (wet basis)82 %
Water-to-solids ratio0.219512 kg/kg
Water held in cake18 kg
  • !Wet basis ≠ dry basis: wet-basis moisture divides water by the TOTAL wet cake; dry-basis moisture divides the same water by the DRY solids, so the dry basis is always the larger number. State which basis you mean.
  • !A mass split of a MEASURED cake — it does NOT predict the moisture a filter will achieve, model dewatering kinetics, or design/select a filter. Cake moisture is a measured input.

Preliminary, formula-based mass split of a measured filter cake into moisture on both bases, cake % solids, the water-to-solids ratio, and the water held in the cake. Not a moisture predictor, a dewatering-kinetics model, or a filter design/selection tool. Cake moisture is a property of the measured cake, not a predicted value.

Related: Filter Cake Moisture Explained · Filtration Mass Balance · Percent Solids Mass ↔ Volume · Hydromet & Slurry Calculations

Formulas

Water held in cake
m_w = m_wet − m_dry
Wet-basis moisture
M_w = (m_wet − m_dry) / m_wet
Cake % solids (wet basis)
S_w = m_dry / m_wet = 1 − M_w
Dry-basis moisture
M_d = (m_wet − m_dry) / m_dry
Water-to-solids ratio
m_w / m_dry

Diagram

Filter cake moisture — wet basis vs dry basis from a wet/dry mass splitwet cake = 100dry solids (82)water (18)wet basis: water / wet cake = 18/100 = 18.0%dry basis: water / dry solids = 18/82 = 21.95%cake % solids = 1 − wet moisture = 82.0%mass split of a measured cake — not a moisture predictor

Worked example

A filter-cake sample weighs 100 kg wet and 82 kg after oven-drying to constant mass. Find the moisture on both bases, the cake % solids, and the water-to-solids ratio.

  1. 01Water held in cake: m_w = 100 − 82 = 18 kg
  2. 02Wet-basis moisture: M_w = 18 / 100 = 18.0%
  3. 03Cake % solids: S_w = 82 / 100 = 82.0% (= 100 − 18.0)
  4. 04Dry-basis moisture: M_d = 18 / 82 = 21.95%
  5. 05Water-to-solids ratio: 18 / 82 = 0.220 kg water per kg solids
Result

Wet-basis moisture 18.0%, cake solids 82.0%, dry-basis moisture 21.95%, water-to-solids ratio 0.220 — note the wet and dry bases differ for the same cake.

FAQ

What is the difference between wet-basis and dry-basis moisture?
Wet-basis moisture divides the water by the TOTAL wet cake mass (water ÷ wet cake); dry-basis moisture divides the same water by the DRY solids mass (water ÷ dry solids). For the same cake the dry basis is always the larger number — 18% wet basis is 21.95% dry basis in the worked example. Always state which basis you mean.
How does cake moisture relate to cake percent solids?
On the wet basis they are complements: cake % solids = 100% − wet-basis moisture. An 18% wet-basis moisture cake is 82% solids. The percent solids and the wet-basis moisture are the same information expressed two ways; the dry-basis moisture is the third, different, way of stating it.
Which basis do filter vendors and metallurgists use?
Mineral-processing practice most often quotes cake moisture on the WET basis (water as a fraction of total wet cake), which is why this calculator leads with it and shows the cake % solids alongside. Drying and some chemical contexts use the dry basis. The mismatch is a frequent reporting error — this page shows both so the value cannot be misread.
Does this predict the moisture my filter will produce?
No. It is a mass split of a cake you have already measured (wet mass and bone-dry mass). It does not predict the moisture a vacuum or pressure filter will achieve on your ore — that depends on the material, cake thickness, air/pressure, cycle time, and washing, and needs filtration testwork. Cake moisture here is a measured input, not a prediction.
What is the water-to-solids ratio?
It is the mass of water per unit mass of dry solids in the cake (m_water ÷ m_dry). Numerically it equals the dry-basis moisture expressed as a ratio rather than a percent — 0.220 corresponds to 21.95% dry basis. It is handy when you want kilograms of water carried per kilogram of product solids.

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