PipeData

Buttweld Fitting Dimensions — B16.9

Centre-to-end dimensions for elbows, returns, tees, crosses, reducers and caps, NPS 1/2 through NPS 24. Because ASME B16.9 dimensions depend on nominal size alone, one table covers every schedule.

90° Long Radius ElbowCentre-to-end A21 sizes90° Short Radius ElbowCentre-to-end A19 sizes45° Long Radius ElbowCentre-to-end B21 sizes180° Long Radius Return BendCentre-to-centre O21 sizesStraight TeeCentre-to-end C and M21 sizesReducing TeeRun centre-to-end C21 sizesStraight CrossCentre-to-end C21 sizesConcentric ReducerEnd-to-end H20 sizesEccentric ReducerEnd-to-end H20 sizesCapLength E21 sizes
90° long radius elbowOutline of a 90 degree long radius elbow. Dimension A runs from the point where the two end centrelines cross to the face of each end. From NPS 1 upward it equals the centreline bend radius of 1.5 times the nominal pipe size.AARadius = 1.5 × NPS (NPS 1 up)90° Long Radius Elbow
90° short radius elbowOutline of a 90 degree short radius elbow. Dimension A runs from the point where the two end centrelines cross to the face of each end, and equals the centreline bend radius of 1.0 times the nominal pipe size.AARadius = 1.0 × NPS90° Short Radius Elbow
45° long radius elbowOutline of a 45 degree long radius elbow. Dimension B runs from the point where the two end centrelines cross to the face of each end.BB45°45° Long Radius Elbow
180° long radius return bendOutline of a 180 degree return bend. Dimension O is the distance between the centrelines of the two ends. Dimension K is the distance from the back of the bend to the end faces.OKO = centre to centreK = back to face180° Long Radius Return Bend
Straight teeOutline of a straight tee. Dimension C runs from the centre of the fitting to the face of each run end. Dimension M runs from the centre to the face of the outlet.CCMStraight Tee
Reducing teeOutline of a reducing tee, with an outlet smaller than the run. Dimension C runs from the centre to the face of each run end. Dimension M runs from the centre to the face of the outlet.CCMReducing Tee
Straight crossOutline of a straight cross, with four ends of the same size. Dimension C runs from the centre of the fitting to the face of each end.CCCStraight Cross
Concentric reducerOutline of a concentric reducer. Both ends share one centreline. Dimension H is the length from end face to end face.HLarge endSmall endConcentric Reducer
Eccentric reducerOutline of an eccentric reducer. One side is flat, so the centrelines of the two ends are offset. Dimension H is the length from end face to end face.Flat sideHLarge endSmall endEccentric Reducer
Buttweld capOutline of a buttweld cap. Dimension E is the overall length from the welding end to the crown of the cap.EWelding endCap
The ten buttweld fittings on this site. Each letter is the dimension ASME B16.9 tabulates for that fitting: A and B for elbows, O and K for return bends, C and M for tees and crosses, H for reducers and E for caps. Not to scale.

Fittings side by side

The governing dimension of each fitting at four common sizes.

Dimensions are given in inches, with the millimetre equivalent beneath in grey.

Governing ASME B16.9 dimension by fitting type. Each column is the fitting's own dimension — centre-to-end for elbows, tees and crosses, centre-to-centre for 180° returns, end-to-end for reducers, length for caps.
FittingNPS 2NPS 6NPS 12NPS 24
90° Long Radius Elbow3.0076.20 mm9.00228.60 mm18.00457.20 mm36.00914.40 mm
90° Short Radius Elbow2.0050.80 mm6.00152.40 mm12.00304.80 mm24.00609.60 mm
45° Long Radius Elbow1.3835.05 mm3.7595.25 mm7.50190.50 mm15.00381.00 mm
180° Long Radius Return Bend6.00152.40 mm18.00457.20 mm36.00914.40 mm72.001828.80 mm
Straight Tee2.5063.50 mm5.62142.75 mm10.00254.00 mm17.00431.80 mm
Reducing Tee2.5063.50 mm5.62142.75 mm10.00254.00 mm17.00431.80 mm
Straight Cross2.5063.50 mm5.62142.75 mm10.00254.00 mm17.00431.80 mm
Concentric Reducer3.0076.20 mm5.50139.70 mm8.00203.20 mm20.00508.00 mm
Eccentric Reducer3.0076.20 mm5.50139.70 mm8.00203.20 mm20.00508.00 mm
Cap1.5038.10 mm3.5088.90 mm6.00152.40 mm10.50266.70 mm

Guides and comparisons for fittings

Long radius vs short radius elbowSpace saved against pressure drop added.90° vs 45° elbowCentre-to-end dimensions and when two 45s beat one 90.Concentric vs eccentric reducerWhich reducer goes where, and which way up.Pipe end connectionsBevelled, plain and threaded ends, and where each is used.

Common questions

Do buttweld fitting dimensions depend on the pipe schedule?

No. ASME B16.9 fixes every centre-to-end dimension from NPS alone. Schedule changes the wall thickness and the bore, not the geometry, so a schedule 10 and a schedule 160 elbow of the same size occupy exactly the same space.

What is the difference between a long radius and short radius elbow?

The centreline bend radius. A long radius elbow bends on 1.5 × NPS, a short radius on 1.0 × NPS. Long radius is the default: it costs less pressure drop and erodes more slowly. Short radius is a space-saving compromise.

Which way up does an eccentric reducer go?

Flat side up on pump suction, so vapour cannot collect at the high point and cavitate the pump. Flat side down on horizontal runs that must drain, so liquid cannot pool. Getting this backwards is one of the more common piping errors.