How to Measure for Window Security Bars
Direct answer: Measure the clear width (inside jamb to inside jamb) at the narrowest point. That single number determines which bar model you need. Height determines how many bars. The entire process takes 3 minutes and requires only a tape measure.
Marcus Reid · IDA Certified
7 minutes
The Two Measurements You Need
Window security bars require exactly two measurements:
Inside jamb to inside jamb, measured at the narrowest point. This determines which model you need.
Inside sill to inside top frame. This determines how many bars you need for full coverage.
Critical rule
Always measure the clear opening — the empty space inside the frame. Never measure the outside frame or the glass pane. Measure at the narrowest point if the opening is not perfectly square.
Step-by-Step Measurement
Open the window fully to access the frame interior
Hold the tape measure horizontally from inside jamb to inside jamb at the narrowest point — record this as your WIDTH
Hold the tape measure vertically from inside sill to inside top frame — record this as your HEIGHT
Compare WIDTH to SWB models: 26"–42" = Model A | 42"–66" = Model B
Determine bar count: one bar for HEIGHT under 12" | two bars for 12"–24" | three bars for over 24"
Common US Window Sizes & Model Fit
| Window Type | Typical Clear Width | SWB Model |
|---|---|---|
| Single-hung / double-hung (standard) | 24"–36" | Model A |
| Single-hung / double-hung (wide) | 36"–42" | Model A |
| Casement window | 20"–32" | Model A |
| Sliding window | 36"–60" | Model A or B |
| Picture window (small) | 30"–42" | Model A |
| Picture window (large) | 42"–66" | Model B |
| Basement hopper | 24"–36" | Model A |
| Sliding glass door panel | 36"–66" | Model B |
What If Your Window Is an Odd Size?
90% of US residential windows fall within the Model A or Model B adjustable range. For the remaining 10%:
Under 26" wide
Most security experts recommend window film + alarm sensor for very narrow windows. Bars below 26" leave insufficient frame material for secure bracket anchoring.
Over 66" wide
Contact SWB for a custom configuration or install two overlapping bars with a center bracket.
Non-rectangular (arched, angled)
Custom fabricated bars are required. SWB can quote custom configurations; lead time is typically 5–7 business days.
Quick Reference
Model A: 26"–42" clear width · $99 · fits most residential windows
Model B: 42"–66" clear width · $129 · wide-span and sliding doors