How this calculator works
Gutters come in lengths of 2, 3 or 4 metres, so the number to buy is the run divided by the length, rounded up. Each join between two lengths needs a union bracket, and the gutter is held by a fascia bracket every 600 to 1,000 mm, depending on the system. Each run has a stop end at both ends, each downpipe needs an outlet in the gutter, and the downpipe is made of 2.5 m lengths held by a clip about every 1.5 m. The gutter must fall towards the outlet at no less than 1 in 600.
Worked example: 12 m of gutter in one run, in 4 m lengths, takes 3 gutters and 2 unions. With a bracket every 800 mm that is 16 fascia brackets, with 2 stop ends and 1 outlet. A downpipe 5 m high takes 2 lengths of 2.5 m and 4 clips, with 1 shoe. The gutter has to fall 20 mm along its length at 1 in 600 (34 mm at 1 in 350). With a bracket every 600 mm the run takes 21 brackets. A 6 m run on a 2.5 m high eave needs 2 gutters and 1 length of downpipe, and a 20 m run with two downpipes takes 5 gutters, 26 brackets and 4 downpipe lengths. Two runs of 18 m in all, with two corners and two downpipes, take 5 gutters and 4 stop ends.
Parts for common runs of guttering (4 m lengths, one run, 800 mm bracket spacing, one downpipe, 5 m high)
Gutter lengths, joints, brackets and the fall at 1:600.
| Run of gutter | Gutters | Joints | Brackets | Fall at 1:600 |
|---|---|---|---|---|
| 4 m | 1 | 0 | 6 | 6.7 mm |
| 6 m | 2 | 1 | 9 | 10.0 mm |
| 8 m | 2 | 1 | 11 | 13.3 mm |
| 10 m | 3 | 2 | 14 | 16.7 mm |
| 12 m | 3 | 2 | 16 | 20.0 mm |
| 16 m | 4 | 3 | 21 | 26.7 mm |
| 20 m | 5 | 4 | 26 | 33.3 mm |
Tips before you buy
- Measure the run along the fascia, not the roof, and add a little for the corners and the stop ends.
- Set the highest bracket first, then run a string line to mark the fall. Half a millimetre of error does not matter: a puddle in the gutter does.
- Use a bracket every 600 to 1,000 mm, depending on the system, and put one close to every joint, outlet and corner.
- Leave a gap of 5 to 10 mm at each union to let the plastic expand in the sun. The joint is sealed by the rubber lip.
- Fit the gutter so that the roof edge overhangs the middle of it, so the water from the tiles falls in.
Tools & materials for this project
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Frequently asked questions
How many lengths of guttering do I need?
Divide the run by the length of each gutter and round up: 12 m of gutter in 4 m lengths is 3 gutters, with 2 unions.
How many gutter brackets do I need?
One every 600 to 1,000 mm, depending on the system, plus one near each end: 16 for 12 m at 800 mm, or 21 at 600 mm.
What fall does a gutter need?
At least 1 in 600, and 1 in 350 is better: 20 mm over 12 m at 1 in 600, and 34 mm at 1 in 350.
How many downpipes do I need?
At least one for each run of gutter, and a long run or a large roof needs more. Ask the supplier, or check the instructions for the system, if the roof is big.
How many downpipe clips do I need?
About one every 1.5 m, and never more than 1.8 m apart, and at least two for each pipe: 4 for a downpipe 5 m high.
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Estimates only. Results assume standard materials and simple shapes. Supplier products vary, and the final call on quantity, structure and safety is yours. Check your local code and your supplier's guidance before ordering.