# How do you calculate the R value of a door?

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## How is R-value calculated?

R-values can be calculated by dividing the thickness of a material (in metres) by its thermal conductivity (k-value or lambda value (λ) in W/mK). R-values are therefore expressed in m2K/W (or ft2·°F·hr/Btu in the USA).

## What is the R-value of a hollow core door?

Here is a simple chart to help understand how R-value is calculated for windows and doors:

WINDOWS R-VALUE
DOORS R-VALUE
Wood Hollow Core (1-3/4”) 2.17
Solid Core Flush (1-3/4”) 3.03
(2-1/4”) 3.70

## What is the unit of R-value?

The R-Value is an imperial system unit of measurement (ft2·°F·h/BTU) and the RSI Value is a metric system unit of measurement (m2·K/W). The higher the resistance value, the slower the rate of heat transfer through the insulating material.

## What is the R-value of 5/8 drywall?

Tables of Building Material R-values

Material Thickness R-value (F° · sq.ft. · hr/Btu)
Building Board
Gypsum Wall Board 1/2″ 0.45
Gypsum Wall Board 5/8″ 0.5625
Plywood 1/2″ 0.62

## What Windows R-value is best?

A good R-value range: Greater than R-5. A good U-value range: 0.20 – 1.20 according to energy.gov.

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