By Evan Christensen · Owner, The Barn Door Hardware Store
Published September 25, 2024 · Updated May 2026
Evan has owned and operated The Barn Door Hardware Store since 2016. Bypass sizing is one of the more commonly miscalculated hardware measurements — and the mistake is almost always the same: using the wrong formula for door width, which produces doors too small to cover the opening. He and the team are available 7 days a week at info@thebarndoorhardwarestore.com.
Bypass barn door sizing works differently from standard single sliding hardware. The door width formula, the overlap calculation, and the track length formula all differ depending on whether you're using single bypass or double bypass — and using the wrong formula produces doors that are either too narrow to cover the opening or a track too short for the doors to fully clear it.
This guide covers the correct formulas for both configurations, with worked examples for common opening sizes. For a full comparison of single vs. double bypass, see our single vs. double bypass guide. Browse our single bypass and double bypass hardware collections.
Single bypass — measuring for 2 doors on one shared track
In a single bypass setup, two doors share one track and slide past each other through a telescoping mechanism. When closed, the doors have a permanent center overlap — the amount depends on the roller style. This overlap must be added to the opening before calculating door width, not subtracted after.
Door width formula
- Standard rollers: Door width = (opening + 10 in) ÷ 2
- Spoke wheel rollers: Door width = (opening + 13 in) ÷ 2
The 10 in and 13 in figures account for: 6 in (standard) or 9 in (spoke) center overlap when closed, plus 4 in total wall overlap (2 in per side). Each door also needs to extend 2 in past the wall on its side to cover the opening completely.
Track length formula
Track length = 3× door width (for a fully clear opening)
Door height
Opening height + 1 in, maintaining 1/2 to 1 in floor clearance at the bottom.
Worked examples — single bypass, standard rollers
| Opening width | Each door width | Track length |
|---|---|---|
| 48 in | (48 + 10) ÷ 2 = 29 in | 3 × 29 = 87 in |
| 60 in | (60 + 10) ÷ 2 = 35 in | 3 × 35 = 105 in |
| 72 in | (72 + 10) ÷ 2 = 41 in | 3 × 41 = 123 in |
| 84 in | (84 + 10) ÷ 2 = 47 in | 3 × 47 = 141 in |
Double bypass — measuring for 2 doors on parallel tracks
In a double bypass setup, two doors run on separate parallel tracks and operate independently. There is no permanent center overlap — the doors fully stack behind each other when pushed to one side. The overlap when closed is at the sides (door over wall), not in the center, and is much smaller than single bypass.
Door width formula
Door width = (opening + 6 in) ÷ 2
The 6 in accounts for 2 in of overlap per side where each door extends past the opening edge over the wall. For bedrooms and bathrooms where privacy is more critical, use (opening + 8 in) ÷ 2 for 3 in overlap per side.
Track length formula
Track length = 3× door width (for a fully clear opening on each track)
Door height
Opening height + 1 in, maintaining 1/2 to 1 in floor clearance at the bottom.
Worked examples — double bypass
| Opening width | Each door width | Track length (each) |
|---|---|---|
| 48 in | (48 + 6) ÷ 2 = 27 in | 3 × 27 = 81 in |
| 60 in | (60 + 6) ÷ 2 = 33 in | 3 × 33 = 99 in |
| 72 in | (72 + 6) ÷ 2 = 39 in | 3 × 39 = 117 in |
| 84 in | (84 + 6) ÷ 2 = 45 in | 3 × 45 = 135 in |
Formula comparison at a glance
| Single bypass (standard rollers) | Single bypass (spoke wheel) | Double bypass | |
|---|---|---|---|
| Each door width | (Opening + 10 in) ÷ 2 | (Opening + 13 in) ÷ 2 | (Opening + 6 in) ÷ 2 |
| Track length | 3× door width | 3× door width | 3× door width (per track) |
| Center overlap when closed | 6 in | 9 in | 2 in center lap (doors overlap each other when closed) |
| Wall overlap per side | ~2 in | ~2 in | ~2 in |
Other measurements to confirm before ordering
- Wall clearance for stacking. When both doors are pushed to one side, confirm there's enough clear wall space for the stack. For double bypass, the stack is approximately one door width. For single bypass, the stack is slightly wider due to the offset required by the telescoping mechanism.
- Ceiling clearance above the opening. Bypass hardware has different clearance requirements than standard sliding hardware. For single bypass: 5 in (straight strap), 6 in (J-strap), 8 in (spoke wheel). For double bypass: 8 in for all hanger styles except spoke wheel, which requires 9-1/2 in. Measure ceiling clearance before selecting a hanger style.
- Header board. Both single and double bypass require a 1×6 hardwood header board (oak, maple, or poplar — not pine) spanning the full track length, secured into wall studs.
- Floor guide. Single bypass kits include one floor-mounted guide for each flat hanger style, and one U-channel guide for each bent or bypass hanger style. The U-channel guide attaches to the inner door and constrains both doors over greater distances without creating a tripping hazard on the floor. For double bypass, a floor-mounted guide is included. Note that double bypass floor guides are typically positioned in the center of the opening where no wall is available — a wall-mounted floor guide is not a practical alternative for double bypass installations. Browse our floor guides collection.
For the full pre-order measurement checklist, see our complete measuring guide.
Want us to verify your measurements before ordering?
Email us at info@thebarndoorhardwarestore.com with your opening width, configuration preference (single or double bypass), and ceiling clearance above the opening — we'll confirm the correct door width and track length before anything ships. Browse our single bypass and double bypass hardware collections. Available 7 days a week.
