What is the 45° offset multiplier?

1.414. Multiply the offset (centre to centre between the two pipes) by 1.414 to get the travel — the centre-to-centre length of the angled piece. With 22½° fittings it is 2.613, with 60° fittings 1.155 and with 11¼° fittings 5.126.

How do I get the cut length from the travel?

Take the fitting take-off off each end. The take-off is how far the fitting adds past the end of the pipe, centre to pipe end, and it is on the fitting maker’s sheet — or measure a fitting you have: from its centre line to where the pipe end stops inside it. Two fittings, so cut = travel − 2 × take-off.

How do I work a rolling offset?

A rolling offset moves up and sideways at once. Measure the rise and the roll (the sideways move) square to the run; the true offset is the diagonal, √(rise² + roll²). Then use that true offset exactly like a plain offset. Type the roll in the optional field and the calculator does the diagonal.

How far along the run the offset travels — the distance between the centres of the two fittings measured parallel to the pipe. At 45° it equals the offset; at 22½° it is 2.414 times the offset, which is why shallow fittings need room.

Pipe offset calculator

Offset (centre to centre)

Fractions welcome: 14 1/2 or 1' 2 1/2".

Fittings

Take-off per fitting (optional)

Centre of the fitting to the end of the pipe in it — from the fitting maker’s sheet.

Roll — for a rolling offset (optional)

The sideways move, measured square to the run. Leave empty for a plain offset.

— cut length

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Trig on the numbers you type. Slope, support spacing, cleanouts and which fittings are allowed where come from your plumbing code and your drawings, not from this page.

Type the offset, pick the fittings and — if you want the length to cut — the take-off of one fitting. You get the travel (centre to centre of the angled piece), the cut length with both take-offs removed, and the advance: how far along the run the offset will land. A rolling offset works the same once the roll is in.

Worked example

A drain has to drop 12 inches with a pair of 45s. Travel = 12 × 1.414 = 16 31/32″, and at 45° the advance equals the offset: 12″. The 45s take off 1¼″ each, so the pipe to cut is 16.97 − 2.5 = 14.47″ — 14 1/2″ to the nearest sixteenth.

Rolling: up 9″ and over 12″. The true offset is √(9² + 12²) = 15″, travel 15 × 1.414 = 21 7/32″, and the fittings roll so the angled piece lies along that diagonal.

Try one

Quick referencefor pipe offsets

Travel: offset × multiplier · 11¼° 5.126 · 22½° 2.613 · 45° 1.414 · 60° 1.155
Advance: offset × factor · 11¼° 5.027 · 22½° 2.414 · 45° 1.000 · 60° 0.577
Cut: travel − 2 × fitting take-off
Rolling: true offset = √(rise² + roll²), then as above

The formula

travel = offset ÷ sin θ · advance = offset ÷ tan θ · cut = travel − 2 × take-off

Questions

What is the 45° offset multiplier?: 1.414. Multiply the offset (centre to centre between the two pipes) by 1.414 to get the travel — the centre-to-centre length of the angled piece. With 22½° fittings it is 2.613, with 60° fittings 1.155 and with 11¼° fittings 5.126.
How do I get the cut length from the travel?: Take the fitting take-off off each end. The take-off is how far the fitting adds past the end of the pipe, centre to pipe end, and it is on the fitting maker’s sheet — or measure a fitting you have: from its centre line to where the pipe end stops inside it. Two fittings, so cut = travel − 2 × take-off.
How do I work a rolling offset?: A rolling offset moves up and sideways at once. Measure the rise and the roll (the sideways move) square to the run; the true offset is the diagonal, √(rise² + roll²). Then use that true offset exactly like a plain offset. Type the roll in the optional field and the calculator does the diagonal.
What is the advance?: How far along the run the offset travels — the distance between the centres of the two fittings measured parallel to the pipe. At 45° it equals the offset; at 22½° it is 2.414 times the offset, which is why shallow fittings need room.

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