---
title: "Wood EMC Calculator"
description: "Equilibrium moisture content from temperature and RH (Hailwood–Horrobin, Simpson 1973)."
image: "https://nestingcalc.com/og-default.png"
url: "https://nestingcalc.com/emc-calculator/"
locale: "en"
---

# Wood EMC Calculator

Equilibrium moisture content from temperature and RH (Hailwood–Horrobin, Simpson 1973).

Enter the air temperature (°C) and relative humidity (0–100%). The calculator returns the EMC on the desorption branch (drying) using Simpson's four-constant form of the Hailwood–Horrobin sorption equation, matched to the Wood Handbook 2021 Table 4-2. Optional reverse mode: enter a target MC and the tool returns the RH you need at the given temperature (useful for kiln operators: 'what RH at 60 °C hits 8% MC?').

Interactive calculator (open in browser): [https://nestingcalc.com/emc-calculator/](https://nestingcalc.com/emc-calculator/)

## FAQ

What is EMC and why does it matter?

EMC (equilibrium moisture content) is the moisture content wood will eventually reach when stored in a given climate. If you build furniture at 12% MC and ship it into a 9% EMC room, the wood loses another 3 pp and may shrink/crack; into a 15% EMC room it swells. Match the build MC to the in-service EMC, not to a fixed number.

Why does desorption sit above adsorption?

Sorption hysteresis: at the same RH, wood that is drying holds more water than wood that is absorbing water from a dry state. The difference is 1–2 percentage points MC across the practical range. For kiln schedules you should use the desorption curve (the high one).

Is the formula accurate at high temperature?

The Simpson 1973 constants are fitted to the −20 °C to +95 °C range; above 100 °C EMC collapses to very small values and the math is less accurate. For high-temperature kiln schedules above 100 °C, treat the answer as a guide and verify against a moisture meter.

## Related calculators

-   [Wood Moisture Content Calculator](https://nestingcalc.com/moisture-content-calculator/)

    MC, basis conversion and drying-outcome — Wood Handbook 2021 equations.

-   [Wood Shrinkage Calculator](https://nestingcalc.com/wood-shrinkage-calculator/)

    Tangential, radial and volumetric shrinkage by species — Wood Handbook 2021 Eq. 4-9.

-   [Kiln Capacity Calculator](https://nestingcalc.com/kiln-capacity-calculator/)

    Wood volume per charge from stack size, board thickness and sticker thickness (AH-188).

## Related guides

-   [EMC and Wood Storage: Why Your Lumber Rack Has a Hygrometer](https://nestingcalc.com/guides/wood-emc-and-storage/)

    Equilibrium moisture content, the Hailwood-Horrobin sorption curve, and how to keep your stock at the MC you dried it to.

-   [Wood Moisture Content: the Number Behind Every Kiln Schedule](https://nestingcalc.com/guides/wood-moisture-content-basics/)

    What MC actually means, why it is not the same as water weight, and how to use it for shipping, drying and inventory decisions.

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