VriksaiTimber IntelligenceBrowse all tools
Home / Wood Selection & Material Science / Fiber Saturation Calculator
Vriksai Timber Intelligence

Fiber Saturation CalculatorFSP and Bound Water Analysis

Determine the Fiber Saturation Point - the critical moisture level where wood begins to shrink and its strength starts to change. Analyse bound water, free water and the state of your timber.

FSP by SpeciesBound vs Free WaterShrinkage OnsetStrength TransitionPDF Report
FSP

Fiber Saturation Calculator

FSP and Bound Water Analysis

Wood and Moisture

Sets typical FSP for the species.

% MC

Typical 26-30%. Adjustable per measurement.

%

Measured MC of the wood.

Optional Sample Mass (for FSP determination)
grams

Leave 0 to skip mass-based MC.

grams

After drying at 103 C to constant weight.

deg C

FSP drops ~0.1%/C above 20C.

OK
Fiber Saturation Analysis
-
% MC
Adjusted FSP
-
state
Water State
-
% MC
Free Water
-
% MC
Bound Water
PropertyValueMeaning
FSP Analysis
About Fiber Saturation Calculator
The Fiber Saturation Point (FSP) is the moisture content at which the cell walls of wood are completely saturated with bound water but the cell cavities hold no free water. It is the single most important threshold in wood science: above FSP wood does not shrink or change strength; below FSP wood shrinks, gains strength and becomes workable. FSP is typically 26-30% MC.
Where Is This Used?
Drying Process ControlWood Science ResearchStrength EngineeringPreservative TreatmentQuality LabsEducation + Training
Formulas Used
MC from mass = (Wet mass - Oven-dry mass) / Oven-dry mass x 100FSP temperature adjust = FSP_20 - 0.1 x (T - 20) (T in deg C)Free water (above FSP) = max(0, MC - FSP)Bound water = min(MC, FSP)Below FSP: shrinkage and strength changes begin
Frequently Asked Questions
Why does wood only shrink below FSP?
Above FSP, water sits freely in the cell cavities and removing it does not change cell wall dimensions. Below FSP, water is bound within the cell walls themselves - removing it causes the walls to pull closer together, which is what we see as shrinkage. This is why all dimensional movement happens below FSP.
Does wood get stronger as it dries below FSP?
Yes, dramatically. As bound water leaves the cell walls below FSP, the wood substance becomes stiffer and stronger. Most strength properties roughly double from green (above FSP) to 12% MC. This is why structural timber must be dried, and why MC must be specified in engineering.
Why does FSP change with temperature?
FSP decreases by roughly 0.1% MC per degree C as temperature rises. In a hot kiln (70C), the effective FSP can drop to ~23% from 28% at room temperature. This affects when shrinkage begins during drying and is important for setting kiln schedules.
ResourcesView the formulasWood Species DatabaseFormula Library
Related Wood Selection tools
More tools in this category
EMC CalculatorEquilibrium moisture content from temp and humidityShrinkage PredictorRadial, tangential and volumetric shrinkageGreen Weight CalculatorWeight of green timber by volume and speciesKiln Schedule FinderDrying time and temperature schedule