Inputs
Example Data
| Method | Inputs | Moisture Content | Typical Use Note |
|---|---|---|---|
| Oven-dry | Wet 2.650 kg, Dry 2.250 kg | 17.78% | Sheltered framing, allow acclimation. |
| Meter (corrected) | Reading 14.0%, Temp -2%, Species +3% | 14.28% | Interior joinery preparation checks. |
| Estimated EMC | 27C, RH 55% | Approx 10-12% | Expected equilibrium, not instant MC. |
Formula Used
1) Oven-dry (gravimetric) moisture content
MC (%) = ((Wwet - Wdry) / Wdry) x 100
- Wwet: mass before drying
- Wdry: oven-dry mass (reference mass)
2) Corrected meter reading (practical field model)
MCcorr = MCmeter x (1 + CT/100) x (1 + CS/100)
- CT: temperature correction (%)
- CS: species/grade correction (%)
3) Estimated EMC from air conditions (Hailwood-Horrobin form)
Uses temperature and relative humidity to estimate equilibrium moisture content (EMC). It helps predict where timber moisture will settle over time in a given environment.
How to Use This Calculator
- Select the method that matches your measurements.
- Enter inputs (masses, meter reading, or air conditions).
- Click Calculate to show results above the form.
- Review condition band for construction decisions.
- Export CSV/PDF for site records and logs.
Professional Notes
1) Why moisture content controls timber performance
Timber is hygroscopic, meaning it exchanges moisture with surrounding air. As moisture content changes, boards shrink or swell across the grain, influencing straightness, joint tightness, and finish quality. Many interior installations target roughly 8–12% moisture, while sheltered structural members often perform well below about 19%.
2) Interpreting oven-dry results for construction decisions
The oven-dry method provides the reference measurement because it compares wet mass to oven-dry mass. This calculator applies MC = ((Wwet − Wdry) / Wdry) × 100. A result near 18% may be suitable for protected framing, but it can still cause visible gaps if installed in conditioned spaces without acclimation.
3) Using corrected meter readings responsibly
Moisture meters are fast for site checks, but readings vary with temperature, species, density, and contact quality. The correction factors in this tool help standardize results for reporting: MCcorr = MCmeter × (1 + CT/100) × (1 + CS/100). Use manufacturer charts whenever possible and retest multiple points along the member.
4) EMC estimation links site climate to expected moisture
Equilibrium moisture content (EMC) estimates where timber moisture will settle after acclimation under steady temperature and relative humidity. If your measured moisture is much higher than EMC, expect drying and shrinkage. If it is far lower, the member may gain moisture and swell, affecting tolerances and coatings.
5) Recording, exporting, and reducing defects
Consistent logging reduces rework. Capture sample IDs, species, and location, then export CSV/PDF for inspection files. Practical thresholds used here highlight risk: below 12% is typically interior-ready, 12–19% is a common service range, 19–28% suggests caution, and above 28% indicates high movement potential during drying.
FAQs
1) Which method should I use on site?
Use meter checks for quick screening, then verify critical members with oven-dry testing when accuracy matters. For planning acclimation, use EMC to understand the environment’s expected moisture level.
2) What does “service range” mean in the result?
It indicates moisture levels commonly acceptable for sheltered construction where minor movement is manageable. Always confirm against project specifications, climate, and the timber’s final service environment.
3) Why can meter readings differ between boards?
Species, density, grain direction, temperature, and contact pressure influence readings. Take multiple measurements along the board, avoid knots when possible, and apply corrections based on meter guidance.
4) Can I use EMC as the actual moisture content?
EMC is an estimate of the long-term equilibrium under steady air conditions. It does not replace direct measurement, especially for freshly delivered or wet timber that is still drying.
5) What is the fiber saturation point and why is it important?
Around 25–30% moisture, cell walls are saturated and extra water is mostly free water. Above this zone, timber can still shrink significantly as it dries below saturation.
6) How many samples should I record for a delivery?
For consistent lots, sample multiple members from different bundles and measure several points per member. Increase sampling for critical finishes, high-value joinery, or if readings vary widely.
7) What should I do if moisture is too high for installation?
Store timber with airflow, keep it off the ground, protect from rain, and allow acclimation toward the room’s EMC. Recheck moisture before installation and document the readings for quality control.