Understanding your result
The headline is the number of clips, and the line under it gives the rows, the clips per row, the pieces of hat channel and the sheets of board. The tiles give the channel, the load per clip and the sheets.
The layout follows the clip makers’ rules. Rows of channel run across the joists, the first and last within 6 in of the walls and the rest at 24 in (16 in for three layers of board). Along each row, clips sit on joists at the spacing you chose, rounded down to a whole number of joist spaces, so 48 in on 16 in joists means every third joist.
The load per clip is the weight of the board divided by the number of clips. The note compares it with a design load published by a common clip maker. If your load is close to or over it, close the clip spacing; if you have a different clip, check its own rating. The insulation between the joists is on the insulation calculator, damping between the layers on the Green Glue calculator, and the cheaper channel-only option on the resilient channel calculator.
How we calculate this
Spacing limits and the design load are from published clip installation guides: clips at most 48 in apart on the channel, rows at most 24 in apart for one or two layers and 16 in for three, a design load of 36 lb per clip for one widely used clip, and channel splices overlapped 6 in between clips. Board weight is the 2.2 lb per sq ft of 5/8 in type X from the sheet weights table. Isolated ceilings that also carry a fire rating must follow a listed assembly; the clip makers point to UL for those.
The assumptions behind the numbers
| Assumption | Default | Where it comes from |
|---|---|---|
| Clip spacing along channel | 48 in maximum | Clip makers’ installation guides (PAC RSIC, Pliteq GenieClip) |
| Row spacing | 24 in for 1–2 layers, 16 in for 3 | Clip makers’ installation guides |
| Design load per clip | 36 lb | Published for a common clip (RSIC-1); check yours |
| Clip fastener | At least 120 lb pull-out and shear; no nails | Clip makers’ installation guides |
| Hat channel | 25 ga, 10 ft, 6 in splices | Clip makers’ installation guides; common stock length |
| Board | 5/8 in, 2.2 lb per sq ft | Manufacturer data sheets |
Assumptions last reviewed October 8, 2026.
The calculator does not give the STC or IIC of the ceiling, which depends on the floor above and the whole assembly; it does not count perimeter isolation or the boxes for light fixtures; and it does not design fire-rated isolated ceilings, which follow a UL listing. How clips, channel, insulation and layers work together against voices and footsteps is in the guide to soundproofing ceilings; the wall equivalent is in the soundproofing basics guide.
Two worked examples
A 20 × 14 ft ceiling, 16 in joists, two layers, clips at 48 in
- Rows: ⌈(168 − 6) ÷ 24⌉ + 1 = 8
- Clips per row: 240 ÷ 48 + 1 = 6; 48 clips
- Channel: 8 × 20 = 160 ft → 18 pieces of 10 ft; board 20 sheets of 5/8 in
- Load: 280 × 2 × 2.2 = 1,232 lb ÷ 48 = 25.7 lb per clip, within 36 lb
Two layers at the maximum spacing is the common build, and it leaves a margin. A third layer at the same spacing would bring each clip close to the limit.
A 12 × 11 ft ceiling, 24 in joists, three layers, clips at 32 in
- Rows at 16 in for three layers: ⌈(132 − 6) ÷ 16⌉ + 1 = 9
- 32 in does not land on 24 in joists, so clips go every joist, 24 in: 7 per row, 63 clips
- Board: 15 sheets; load 871 lb ÷ 63 = 13.8 lb per clip
Three layers on clips every joist is a heavy-duty home-theatre ceiling, and the load per clip is low because there are so many clips.
Where to find your inputs
Ceiling size. The length across the joists and the width along them.
Joist spacing. Centre to centre, from the attic or the exposed framing.
Layers. Two layers of 5/8 in is the usual isolated ceiling; one layer gains less; three is for theatres.
Clip spacing. Start at 48 in and close it if the load check says so.
Common mistakes
- Clips between joists. Clips fix to joists. Space them in whole joist spaces.
- Nailing clips. The makers forbid it. Use the specified screws.
- Board touching the walls. Leave a 1/4 in gap and seal it; contact bypasses the clips.
- Lights on the channel. Fixtures need boxes on the joists, sealed at the board.
- Too heavy for the clips. Three layers at 48 × 24 in can exceed the design load. Check it.
- Channel spliced at a clip. Overlap splices between clips, with screws or wire.
Questions people ask
- How far apart are sound isolation clips?
- Clip makers allow clips up to 48 in apart along the hat channel and rows of channel up to 24 in apart for one or two layers of board, 16 in apart for three layers. Clips are fixed to joists, so the spacing along the channel is a whole number of joist spaces: 48 in on 16 in joists is every third joist.
- How many isolation clips do I need for a ceiling?
- A 20 × 14 ft ceiling on 16 in joists with two layers of board has eight rows of channel and six clips per row at 48 in, 48 clips. The calculator counts your ceiling and checks the load per clip.
- How much weight can an isolation clip hold?
- Makers publish a design load per clip; one widely used clip is rated at 36 lb. Two layers of 5/8 in board weigh about 4.4 lb per sq ft, so at 48 × 24 in spacing (8 sq ft per clip) each clip carries about 35 lb, close to that limit; closer spacing gives a margin.
- Clips or resilient channel for a ceiling?
- Clips with hat channel are more forgiving: the clip does the isolating, so a stray screw into a joist does less harm, and clips carry heavier ceilings. Resilient channel is cheaper and lighter but easy to short. For a ceiling under a living space, clips are the safer choice.
- What screws for isolation clips?
- The clip makers specify a fastener with at least 120 lb of pull-out and shear capacity for fixing each clip to the joist, and not nails. The board is fixed to the hat channel with fine-thread Type S drywall screws long enough for the layers but short of the joists.
- Can I hang lights from an isolated ceiling?
- Light fixtures and fans need boxes fixed to the joists, not to the channel, with a gap and sealant where the board meets the box. Heavy fixtures must not hang from the clips or channel.