Mini-split line set size chart
Short answer: Most mini-splits use one of three line set sizes (liquid × suction): 1/4" × 3/8" at 9,000 BTU, 1/4" × 1/2" at 12,000–18,000 BTU, and 3/8" × 5/8" at 24,000–48,000 BTU. Diameter is set by your system's BTU capacity, not the brand, and line sets come in standard 15, 25, 35, and 50 ft lengths. Always confirm against your unit's installation manual.
The quick reference for ductless line set sizing — diameter by BTU and by brand, plus standard lengths. Want it done for you? Use the size calculator or look it up by brand.
Line set size by mini-split capacity
Line set diameter is set by your system's BTU rating. Match the pair below, then pick your length.
| System size | Line set (liquid × suction) | Shop |
|---|---|---|
| 9,000 BTU (¾ ton) | 1/4" × 3/8" | Shop → |
| 12,000 BTU (1 ton) | 1/4" × 1/2" | Shop → |
| 18,000 BTU (1.5 ton) | 1/4" × 1/2" | Shop → |
| 24,000 BTU (2 ton) | 3/8" × 5/8" | Shop → |
| 36,000 BTU (3 ton) | 3/8" × 5/8" | Shop → |
| 48,000 BTU (4 ton) | 3/8" × 5/8" (some 3/8" × 3/4") | Shop → |
Line set size by line size
Already know your diameters? Here's what each stocked pair fits.
| Line set | Fits these systems | Shop |
|---|---|---|
| 1/4" × 3/8" | 9,000 BTU | Shop → |
| 1/4" × 1/2" | 12,000–18,000 BTU | Shop → |
| 3/8" × 5/8" | 24,000–36,000 BTU (and most 48,000 BTU) | Shop → |
Line set lengths
Length is set by the distance between your indoor head and outdoor condenser. Measure the full routing path — including bends and the drop — then round up to the next stocked length.
| Length | Best for |
|---|---|
| 15 ft | Short runs — same room or just through the wall |
| 25 ft | The most common length — typical wall-to-condenser runs |
| 35 ft | Longer runs, second-story, or units around a corner |
| 50 ft | Maximum reach — distant condenser placement |
On pre-charged DIY systems, watch the maximum pre-charged length (often 25 ft) — longer runs may need refrigerant added by a pro.
Line set size by brand
Diameter is the same across brands for a given capacity — what changes is the connection. Pre-charged quick-connect systems (like MrCool DIY) use proprietary line sets; everything else is field-flared. Look up your exact brand →
Jump straight to a brand guide: Mitsubishi, Daikin, MRCOOL, LG, Fujitsu, or Pioneer.
These are the most common pairings; exact diameters and the maximum line length are always printed in your unit's installation manual — treat it as the final word.
Common questions
What size line set for a 12,000 BTU mini-split?
A 12,000 BTU (1-ton) mini-split typically uses a 1/4" liquid line and a 1/2" suction line — 1/4" × 1/2". Confirm against your unit's manual, since some 12,000 BTU models — including most Mitsubishi and Daikin — use 1/4" × 3/8".
What size line set for a 9,000 BTU mini-split?
A 9,000 BTU (3/4-ton) mini-split uses a 1/4" liquid line and a 3/8" suction line — 1/4" × 3/8". It's the smallest of the three common mini-split line set sizes.
What size line set for an 18,000 BTU mini-split?
An 18,000 BTU (1.5-ton) mini-split typically uses 1/4" × 1/2", the same pair as a 12,000 BTU unit. Confirm your model's manual, since a few larger 18k units step up.
What size line set for a 24,000 BTU mini-split?
A 24,000 BTU (2-ton) mini-split typically uses a 3/8" liquid line and a 5/8" suction line — 3/8" × 5/8". A notable exception is Daikin, which keeps a 1/4" liquid line (1/4" × 5/8"). Confirm your manual.
What size line set for a 36,000 BTU mini-split?
A 36,000 BTU (3-ton) mini-split typically uses 3/8" × 5/8", the same as a 24,000 BTU unit. Some 48,000 BTU (4-ton) systems step the suction line up to 3/8" × 3/4". Confirm your manual.
What are the standard mini-split line set sizes?
The most common ductless line set sizes are 1/4" × 3/8", 1/4" × 1/2", and 3/8" × 5/8" (liquid × suction), sold in standard lengths of 15, 25, 35, and 50 feet.
Does line set size depend on the brand?
No — line set diameter is set by your system's BTU capacity, not the brand, so a 12,000 BTU unit uses the same diameters across most brands. What changes by brand is the connection (field-flared vs. pre-charged quick-connect like MRCOOL DIY) and a few exceptions such as Daikin's 1/4" liquid line. Look up your brand →
How do I measure the line set length I need?
Measure the full routing path between your indoor head and outdoor condenser — including every bend and the vertical drop — then round up to the next stocked length (15, 25, 35, or 50 ft). On pre-charged DIY systems, stay within the maximum pre-charged length (often 25 ft) or have a pro add refrigerant. Use the size calculator →
Line set sizes by brand: Mitsubishi · Daikin · MRCOOL · LG · Fujitsu · Pioneer
This chart provides general guidance based on common mini-split line set sizing. Exact line diameters, connection types, and maximum line lengths vary by model — always verify against the manufacturer's installation manual before purchasing or installing.