Pulp Consistency Calculator
Calculate pulp stock consistency from fiber weight and slurry weight. Determine dilution water needed and fiber flow rates for paper machine approach systems.
About this calculator
Consistency is the paper industry's term for fiber concentration in a pulp slurry — the oven-dry fiber weight expressed as a percentage of the total slurry weight (fiber plus water), and it's one of the most closely watched numbers on a paper machine because it governs how the stock drains, forms, and dewaters. This calculator takes your current dry fiber weight and total slurry weight to compute that percentage directly, then works backward to tell you the total slurry weight — and therefore the water to add or remove — needed to hit a target consistency while holding fiber weight fixed. It also buckets your current reading into the process zones a papermaker would recognize: below 0.1% is white water, 0.1-1.5% is approach-flow/headbox range, 1.5-6% is thick stock from the pulper, 6-15% is medium consistency, and above that is high-consistency stock.
Two supplementary numbers are estimates rather than measurements: fiber mass flow rate (kg/min and tons/day) assumes slurry density rises only slightly above water's as fiber content increases, and estimated wire retention is a simple linear approximation (roughly 70% baseline, rising with consistency) standing in for the fines/filler retention behavior a real furnish and wire configuration would determine. Use those two for rough sizing and trend-checking, not for process control — real retention depends heavily on furnish type, retention aid dosage, and wire design, none of which this calculator models.
Inputs
Results
Current consistency (%)
5
How to Use This Calculator
- Enter the oven-dry fiber weight (kg) in your stock sample or batch.
- Input the total slurry weight (kg) including fiber and water.
- Set the target consistency (%) for the next process stage.
- Enter the stock flow rate (L/min) to calculate fiber throughput.
- Review Current Consistency (%), Water Change needed (L), Fiber Flow (kg/min and t/day), and Consistency Category.
How the result changes with Total slurry weight (kg)
| Total slurry weight (kg) | Current consistency (%) |
|---|---|
| 500 | 10 |
| 750 | 6.67 |
| 1,500 | 3.33 |
| 2,500 | 2 |
What each input means
- Dry fiber weight (kg)
- Oven-dry weight of fiber in the stock sample or batch (kg).
- Total slurry weight (kg)
- Total weight of the fiber + water slurry (kg).
- Target consistency (%)
- Desired consistency for the next process stage.
- Flow rate (L/min)
- Stock flow rate for calculating fiber throughput.
What each result means
- Current consistency (%)
- Current fiber consistency as percentage of total slurry weight.
- Water weight (kg)
- Weight of water in the current slurry.
- Target slurry weight (kg)
- Total slurry weight needed to achieve target consistency with the same fiber.
- Water change (L)
- Water to add (positive) or remove (negative) to reach target consistency.
- Fiber flow (kg/min)
- Bone-dry fiber mass flow rate at current consistency and flow rate.
- Fiber flow (t/day)
- Fiber throughput in metric tons per day.
- Consistency category
- 0 = White water, 1 = Approach/headbox, 2 = Thick stock, 3 = Medium, 4 = High.
- Est. wire retention (%)
- Estimated first-pass retention on the paper machine wire.
How this is calculated
Worked example, using the default values
- Identify Input Parameters4 parametersDry fiber weight (kg) = 50, Total slurry weight (kg) = 1000, Target consistency (%) = 1, Flow rate (L/min) = 500 = 4 input(s) provided
- Calculate Current consistencyCurrent consistency = (dryFiberKg / totalSlurryKg) * 1005 = 5
- Calculate Water weightWater weight = totalSlurryKg - dryFiberKg950 = 950
- Calculate Target slurry weightTarget slurry weight = targetConsistencyPct > 05000 = 5000
Engine last updated . Checked against 2 independently-derived tests — how we verify calculators. Built by Paul Gunder, a software engineer, not a licensed financial, medical, or legal professional.
Frequently Asked Questions
How does the calculator determine how much water to add or remove?
It holds your dry fiber weight fixed and computes the total slurry weight needed to hit your target consistency, using dryFiberKg divided by targetConsistencyPct times 100, then subtracts your current total slurry weight to get the water change — a positive value means add water to dilute, a negative value means remove water to thicken. It assumes water has a density of about 1 kg/L, so the liter figure equals the kilogram figure.
What do the consistency category numbers (0-4) mean?
They map your current consistency percentage onto process zones a papermaker would recognize: below 0.1% is white water, 0.1-1.5% is approach-flow/headbox range, 1.5-6% is thick stock from the pulper, 6-15% is medium consistency, and above 15% is high consistency. These thresholds are fixed inside the calculator, not something you configure.
How reliable is the estimated wire retention figure?
It's a simple linear approximation — a 70% baseline that rises by 5 percentage points for every 1% of consistency, capped at 99%. It's meant for rough sizing and trend comparisons rather than process control, since real first-pass retention depends heavily on furnish type, retention aid dosage, and wire design, none of which this calculator models.
Why does fiber flow rate depend on slurry density if the slurry is mostly water?
The calculator assumes slurry density rises slightly above water's as fiber content increases (1.0 plus consistency percent divided by 100, times 0.5), a small correction since fiber solids are somewhat denser than water. Fiber mass flow is then flow rate times slurry density times the current consistency fraction, so the density correction barely matters at low consistency but becomes more meaningful at higher consistency inputs.
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