Guide · Measuring and buying
How to measure drip tubing before you buy fittings
Read the print first, then measure the outside diameter of a clean cut end and match it to a fitting whose maker states a range that includes it.
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Short answer
Read the print on the tube or the kit's papers first. If there is none, measure the outside diameter of a clean, round, freshly cut end with calipers, then buy a fitting whose maker states a size range that includes your number.
Step 1: read the label or the kit papers
Makers print or document the size, and that beats any measurement. Three examples of what to look for:
- DIG lists its 1/2 in poly tubing as .600 in ID by .700 in OD.[1]
- Raindrip lists its 062010P supply tubing as .620 in ID by .710 in OD.[2]
- Rain Bird names its 1/2 in blank tubing by OD: T63 is 0.63 in, T70 is 0.70 in and T71 is 0.71 in.[3]
If your tubing came in a kit, the kit's instructions often list it. A model number on the tube or the box is enough to look up the maker's page.
Step 2: measure the outside diameter
This is plain shop technique, not a maker procedure:
- Cut a fresh, square end with a sharp tubing cutter or pruners. Old ends are often stretched by a fitting or squashed flat.
- Hold calipers across the outside of the tube without squeezing it out of round.
- Take three or four readings, turning the tube between them, and use the typical value.
We found no maker or extension source that gives a measuring tolerance for drip tubing. Treat a reading between two listed sizes as a question for the fitting's maker, not as a fit.
Step 3: measure the ID only when a fitting is listed by it
Barbed inserts go inside the tube, and some locking fittings are listed both ways. DIG lists its NUTLOC fittings for tubing with a .530, .600 or .620 in ID, described as .630-.710 in OD.[4] For an ID, use the calipers' inside jaws across a clean cut end, or better, take the ID from the maker's ID x OD pair once you know the OD and the brand.
Step 4: match the number to a stated range
| Fitting | Size the maker states | Source |
|---|---|---|
| DIG compression, green insert | .620-.630 in OD | DIG[5] |
| DIG compression, blue insert | .710 in OD | DIG[5] |
| Rain Bird Easy-Fit compression | 0.63-0.70 in OD | Rain Bird[6] |
| Orbit 67466 coupling | .620-.710 in OD | Orbit[7] |
| DIG NUTLOC | .530, .600 or .620 in ID; .630-.710 in OD | DIG[4] |
Fit is the range the maker states. A "1/2 in" label on the fitting alone tells you nothing about your OD.
If you are unsure where your tubing sits, a coupling whose stated range spans all three common sizes removes one guess.
Picks that fit2 products
Orbit lists the 67466 for .620-.710 in OD; Raindrip lists the Smart Loc S5600UB for .520 x .620, .600 x .700 and .620 x .710 in.
More on choosing
Choose one only if your measured OD falls inside its stated range.
Choose the Orbit 67466 for the widest stated OD range
Orbit 67466 1/2 in universal drip coupling (0.620‑0.710 in OD)
Choose the Raindrip Smart Loc S5600UB when you know your ID x OD pair
Raindrip Smart Loc S5600UB universal coupling (0.620, 0.700 and 0.710 in OD)
On Amazon, check that "Ships from / Sold by" is Amazon.com or the brand before you buy.[8]
When the numbers disagree
Some maker numbers do not add up, so use the ID x OD pair, not the extra figures:
- DIG's .710 tubing page prints a wall thickness that does not match its own .620 x .710 pair.[9]
- Rain Bird's XQ 1/4 in tubing sheet gives a wall value that is inconsistent with its 0.17 in ID and 0.25 in OD.[10]
- Raindrip's FAQ gives .620-.630 in as an I.D. for its 1/2 in fittings, while its product pages use .620 as an OD.[11]
When a conflict touches your purchase, ask the maker which number is right.
Metric listings
Metric tubing and fittings are often listed by a pair of numbers such as 4/7 mm, and sellers do not always say which is the ID. AquaGrow's own 4/7 mm tee listing asks buyers to confirm the actual inner and outer dimensions before ordering.[12] Our metric drip tubing guide covers joining metric parts to US tubing.
What to measure, by fitting type
| Fitting type | Measure | Tool |
|---|---|---|
| Compression | OD | Calipers |
| Locking-nut | OD, sometimes ID too | Calipers |
| Barbed insert | ID, or the maker's ID x OD pair | Calipers or the maker's listing |
Next
Questions
How do I measure drip tubing?
Read any print on the tube or in the kit papers first. If there is none, cut a clean, square end and measure its outside diameter with calipers, taking a few readings around the tube.
Do I measure the inside or outside diameter for drip fittings?
Measure the outside diameter for compression and most locking fittings, which are listed by OD. Barbed inserts go inside the tube, and some makers list locking fittings by both; DIG lists NUTLOC by ID (.530, .600 or .620 in) and by OD (.630-.710 in).[4]
Can I measure drip tubing with a ruler?
We found no maker or extension source that gives a measuring method or tolerance. The common 1/2 in sizes differ by as little as 0.01 in (.700 vs .710 in OD), which a ruler cannot resolve, so calipers are the practical tool.
What if my drip tubing has no markings?
Measure the OD of a fresh cut end and compare it to the ranges fitting makers state, such as DIG's .620-.630 in green inserts or Rain Bird Easy-Fit's 0.63-0.70 in. If your reading sits between sizes, ask the fitting's maker before buying.[5][6]
Is metric drip tubing listed by inside or outside diameter?
It varies by seller. AquaGrow's own 4/7 mm listing asks buyers to confirm the actual inner and outer dimensions before ordering.[12]