Calculate the actual door header depth and height from nominal 4×4, 4×6, 4×8, 4×10, or 4×12 sizes in your chosen unit with unit conversion.
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Door Header Size (Actual Dimension) Formula
The calculator uses a nominal-to-actual lumber size lookup, then converts the actual header depth, also called height, into the selected unit.
- Nominal Header Size is the selected lumber size, such as 4×6 or 4×10.
- Actual Depthin is the dressed lumber depth in inches.
- Actual Depthm is the actual depth converted to meters.
- Conversion Factorselected is the number of meters in one selected unit.
- Actual Depthselected is the final actual header depth in the unit you choose.
The calculator first identifies the typical actual depth for the nominal door header size. For example, a nominal 4×8 is typically 7.25 inches deep, not 8 inches. It then converts that actual depth from inches to meters and from meters to the unit selected in the dropdown.
This calculator gives the actual physical dimension only. It does not determine whether a header is strong enough for a wall opening, roof load, floor load, snow load, or code requirement.
Typical Actual Dimensions for Nominal 4× Door Headers
| Nominal Header Size | Typical Actual Thickness | Typical Actual Depth / Height |
|---|---|---|
| 4×4 | 3.5 in | 3.5 in |
| 4×6 | 3.5 in | 5.5 in |
| 4×8 | 3.5 in | 7.25 in |
| 4×10 | 3.5 in | 9.25 in |
| 4×12 | 3.5 in | 11.25 in |
Unit Conversion Factors Used for Header Depth
| Unit | Meters per Unit | How the Calculator Converts from Meters |
|---|---|---|
| inch, in | 0.0254 | meters ÷ 0.0254 |
| foot, ft | 0.3048 | meters ÷ 0.3048 |
| millimeter, mm | 0.001 | meters ÷ 0.001 |
| centimeter, cm | 0.01 | meters ÷ 0.01 |
| yard, yd | 0.9144 | meters ÷ 0.9144 |
Example Calculations
Example 1: Actual depth of a 4×8 door header in inches
Selecting a nominal 4×8 header gives a typical actual depth of 7.25 inches.
The calculator result is 7.2500 in when inches are selected.
Example 2: Actual depth of a 4×10 door header in feet
A nominal 4×10 header has a typical actual depth of 9.25 inches.
The calculator result is 0.7708 ft when feet are selected.
FAQ
Is nominal door header size the same as actual size?
No. Nominal size is the named lumber size, while actual size is the finished dimension after milling and drying. For example, a nominal 4×8 header is typically 3.5 inches thick by 7.25 inches deep.
Does this calculator tell me what size header I need for a door opening?
No. It only converts a selected nominal header size into its typical actual depth. Header sizing for a real opening depends on span, wall type, roof load, floor load, snow load, lumber species, grade, and local building code.
Why is the depth called height in the calculator?
For a header installed above a door, the vertical dimension of the lumber is often called the depth or height. In this calculator, actual depth and actual height refer to the same vertical dimension of the header.
