How to Measure Jamb Depth for Andersen Windows

Measuring the jamb depth of an Andersen window tells you the thickness of the wall frame the window sits in, which is essential when ordering replacement windows, installing new trim, or fitting blinds and shades. You only need a tape measure and a few minutes. This guide walks you through the process for both new construction and replacement-style Andersen windows.

What You’ll Need

Tape measure (metal, at least 25 ft long)
Pencil and paper (or a phone notes app) to record measurements
Flashlight (optional, to see into dark jambs)
A second person (helpful, but not required, for long tape measures)

Step-by-Step

Identify the jamb. The jamb is the vertical or horizontal frame piece that runs along the inside edge of the window opening, between the window sash (the part that opens) and the wall. You are measuring the depth of this piece — the distance from the interior face (the side you see from inside your room) to the exterior face (the side facing outside).
Open the window. If your window has a sash that slides or tilts, open it fully so you can access the full depth of the jamb. For casement windows, crank the sash open. For double-hung windows, lift the lower sash up. If the window does not open (fixed or picture window), you will measure from the interior side only, using the method in step 4.
Position the tape measure. Place the end of the tape measure flat against the interior edge of the jamb (the edge closest to the room). Hold it perpendicular to the jamb, so the tape extends straight back toward the exterior. For most Andersen windows, the jamb is a flat piece of wood or composite; the tape should lie flush against it.
Read the depth. Look at where the jamb meets the exterior wall or the exterior casing. The measurement at that point is your jamb depth. For a standard wood-frame wall, this is typically 3-1/2 inches (for a 2×4 wall) or 5-1/2 inches (for a 2×6 wall). For Andersen 400 series windows, the jamb depth is often 3-3/8 inches for 2×4 walls and 5-3/8 inches for 2×6 walls, but always measure your actual window.
Measure at multiple points. Take the measurement at the top, middle, and bottom of both side jambs, and also across the top and bottom jambs. Walls are rarely perfectly square, and the jamb depth can vary by 1/8 inch or more. Record the smallest and largest readings.
For fixed windows (no sash that opens). If you cannot open the window, measure from the interior side only. Place the tape against the interior face of the jamb and extend it toward the exterior. You will not be able to see the exterior edge, so instead measure the distance from the interior face to the back of the jamb (the point where the jamb meets the window frame or the exterior casing). This gives you the “interior jamb depth,” which is what you need for most replacement purposes. For a true full depth, you may need to measure from the exterior side as well, using a helper or a second tape measure.
Record the measurement. Write down the depth in inches, using fractions (e.g., 3-1/2″) rather than decimals, since Andersen and most window suppliers use fractional measurements. Note whether it is a 2×4 or 2×6 wall based on the depth (3-1/2″ vs 5-1/2″).
Check for existing trim. If your window has interior casing (trim) installed, the jamb depth measurement should be taken from the bare jamb, not from the face of the trim. If the trim overlaps the jamb, measure from the jamb surface, not the trim edge.

Common Mistakes

Measuring from the wrong starting point. Starting from the drywall or the trim instead of the jamb face adds 1/2 to 3/4 inch to your reading. Always start from the jamb itself.
Measuring at an angle. If the tape is not perpendicular to the jamb, you will get a longer (and incorrect) reading. Hold the tape level and square.
Using only one measurement. Walls bow and settle; a single reading can be off by 1/8 inch or more. Always take at least three readings per side.
Confusing jamb depth with frame width. The jamb depth is the thickness of the frame, not the width of the window opening. Do not measure horizontally across the window; measure perpendicular to the wall.
Ignoring the exterior casing. Some Andersen windows have exterior brickmold or casing that extends beyond the jamb. The jamb depth is measured to the exterior face of the jamb, not to the outer edge of the brickmold.

Tips

For Andersen 400 and 200 series windows, the jamb depth is usually a standard size (3-1/2″ or 5-1/2″), but always verify with your own measurement — older homes may have non-standard framing.
If you are ordering replacement windows, provide the jamb depth in inches and fractions, not just the wall type. This helps the supplier match the correct frame.
Use a rigid tape measure (not a cloth one) to avoid sagging and inaccurate readings.
Take a photo of the window with the tape measure in place. This helps if you need to double-check later or show a supplier.
If the window is old and painted shut, measure from the interior side only — you do not need to force the window open just to get a depth reading.
For a 2×4 wall, the rough opening is typically 3-1/2″ deep, but the actual jamb may be slightly less due to drywall or plaster. Measure the jamb itself, not the wall cavity.

Troubleshooting

You cannot see the exterior edge of the jamb. If the window is fixed or the exterior is covered, measure from the interior face to the back of the jamb (where it meets the window frame). This interior depth is usually sufficient for ordering replacement sashes or interior trim. For full-depth measurements, use a thin probe (like a wire) to feel the back edge, or measure from outside.
The measurement varies by more than 1/4 inch between points. This indicates the wall is out of square or the jamb is warped. Record all readings and use the largest one for ordering, but note the variation to the supplier. If you are installing blinds, use the smallest reading to ensure a snug fit.
Your tape measure will not fit into the gap. For very tight spaces, use a thin metal ruler or a caliper. Alternatively, hold a straight edge against the jamb and measure from the straight edge to the exterior — then subtract the thickness of the straight edge.
The window has a nailing fin (flange) on the exterior. This is common on new construction windows. The jamb depth is measured to the interior face of the nailing fin, not to the outer edge of the fin itself. The fin sits on the exterior sheathing, so the jamb depth is the distance from the interior jamb face to the interior face of the fin.
You are measuring a basement window with a deep well. The jamb depth may be deeper than a standard wall (e.g., 7-1/2″ for concrete walls). Measure exactly as described — from interior face to exterior face — and record the actual number, even if it is non-standard.
You need the measurement but the window is covered by storm windows or screens. Remove the storm window or screen if possible. If not, measure the jamb depth from the interior side only, and note that the exterior storm window adds thickness to the overall assembly, not the jamb.

Frequently Asked Questions

Q: What is the standard jamb depth for an Andersen window?
A: For most Andersen 400 and 200 series windows, the standard jamb depth is 3-3/8 inches for a 2×4 wall and 5-3/8 inches for a 2×6 wall. However, older homes and custom installations can vary, so always measure your actual window.

Q: Do I need to measure both sides of the window?
A: Yes. Measure both side jambs, the top jamb, and the bottom jamb. Walls are rarely perfectly uniform, and differences of 1/8 inch are common. Record the largest and smallest readings.

Q: Can I measure jamb depth without opening the window?
A: Yes, for fixed windows or windows that do not open, measure from the interior face of the jamb to the back of the jamb (where it meets the window frame). This gives you the interior jamb depth, which is what most replacement parts need. For a full depth, you would need to measure from outside as well.

Q: Is jamb depth the same as frame depth?
A: Yes, in most cases “jamb depth” and “frame depth” refer to the same measurement — the thickness of the window frame from the interior to the exterior. Some manufacturers use “frame depth” to include exterior trim, so clarify when ordering.

Q: What if my measurement is 3-1/2 inches but Andersen says 3-3/8?
A: The 1/8-inch difference is usually due to drywall or plaster covering part of the jamb. Measure the bare jamb, not the wall surface. If you are ordering replacement parts, give the supplier both the jamb depth and the wall thickness so they can advise.

Q: Do I need to measure jamb depth for replacement windows or just for blinds?
A: Both. For replacement windows, jamb depth ensures the new window fits the existing frame. For blinds and shades, jamb depth tells you the mounting depth available. Always measure before ordering either.

General steps for current mainstream versions; menus can differ by device and version. See the disclaimer or report an error.

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