Guttering Length Calculator

About this calculator

Sizing a guttering job means converting a roof edge’s total length into a shopping list: divide the edge length by the standard length gutters are sold in (commonly 3m or 4m) and round up to get the number of lengths, add a joint union at each point where two lengths meet, and space support brackets at regular intervals (typically every 50–60 cm) along the full run to stop the gutter sagging under the weight of water. Downpipes are then sized separately, based on how many outlets the gutter run has and the total vertical drop each one needs to cover.

Roofers and DIY installers do this math before ordering materials because guttering is sold in fixed lengths, not by the metre, so rounding errors either leave you short mid-installation or paying for offcuts you didn’t need — and underestimating brackets is one of the most common reasons gutters sag and pull away from the fascia within a few years.

This calculator takes your roof edge length, gutter length per piece and bracket spacing, and returns exactly how many gutter lengths, joint unions, brackets and downpipes your job needs, plus the total downpipe run.