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Plant Engineering Calculator

Updated Sep 18, 2026

Cooling Tower L/G Ratio Calculator — Water-to-Dry-Air Mass Ratio

Calculate cooling-tower liquid-to-gas mass ratio from circulating-water and dry-air volumetric flow with entered densities.

Live calculationWorking shownPrivate in browser

Inputs

Results

Liquid mass flow 997000 kg/h
Dry-air mass flow 920000 kg/h
L/G ratio 1.084 kg/kg
G/L ratio 0.923 kg/kg
More actions

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Formula

L/G=(Qwρw)/(Qaρa).

Your calculation, step by step

These steps use the values currently entered above so the result can be checked independently.

  1. 1.Liquid mass flow L = Qw × ρw = 1000.00 × 997.00 = 997000 kg/h.
  2. 2.Dry-air mass flow G = Qa × ρa = 800000 × 1.150 = 920000 kg/h.
  3. 3.L/G = 997000 ÷ 920000 = 1.0837 kg/kg.
  4. 4.Reciprocal G/L = 920000 ÷ 997000 = 0.9228 kg/kg.

How to use this calculator

  1. Enter measured or design values using the units shown beside each field.
  2. Review the live results and the substituted calculation steps before using the estimate.
  3. Check the assumptions below, then continue to a related calculator when the next engineering decision needs another model.

Worked example

1,000 m³/h water and 800,000 m³/h dry air at 1.15 kg/m³ gives L/G about 1.09 kg/kg.

Assumptions and limits

  • Use dry-air mass flow when available; humid-air density varies with weather and altitude.
  • L/G alone does not predict tower approach without transfer characteristics.

How to interpret the result

Treat the primary result as an engineering screening value, then use the secondary outputs to understand scale, energy or operating impact. Confirm site measurements, equipment limits and applicable standards before making a design or control change.

Questions engineers ask

Should cooling-tower L/G use volumetric flow or mass flow?

L/G is a mass-flow ratio. This calculator accepts volumetric water and dry-air flow only because it multiplies each by the entered density first; the displayed liquid and gas mass flows are the values actually used in the ratio.

Why is air density an editable input?

Dry-air density changes with temperature, pressure and altitude. A fixed standard-air assumption can bias the gas mass-flow estimate, so enter a density appropriate to the air-flow basis or use measured dry-air mass flow when available.

Does a lower or higher L/G predict tower approach by itself?

No. L/G is an important operating ratio, but tower approach and capacity also depend on wet-bulb conditions, fill and transfer characteristics, water distribution, fan performance and tower condition.

Continue the calculation

Use the next calculator in the same engineering workflow instead of restarting from search.

cooling tower range approachcooling tower heat rejectioncooling tower water balance
Methodology. MAXScanner shows the governing formula, entered values and calculation outputs so the estimate is auditable. The calculator is a screening aid; assumptions and equipment-specific limits remain part of the engineering review.