Gutter Length Calculator

Gutter length calculator for estimating how much guttering to buy

This gutter length calculator is built for one job: estimating how much gutter you need to purchase for a typical house or small building. If you are standing at a hardware store (or pricing a job), the practical decision is not “what is the perimeter,” it is “how many meters or feet of gutter should I buy so I do not come up short.”

The most reliable way to estimate gutter quantity is to add up the lengths of the roof edges where gutters will actually be installed. Many homes do not place gutters on every edge. For example, a gable roof often has gutters only on the two long eaves, and none on the gable ends. This calculator lets you enter multiple gutter runs, total them, apply a small waste allowance, and then convert that total into a number of standard gutter sections.

The result shows your total required gutter length (including waste), the number of sections to buy based on the section length you choose, and how much “extra” length those sections provide after rounding up. That extra is normal because gutters are bought in fixed lengths. The calculator is intentionally locked to gutter length and section count only. It does not estimate downspouts, brackets, end caps, outlets, angles, miters, guards, or installation labor.

Assumptions and how to use this calculator

• Only include edges where gutters will be installed. Do not assume every roof edge needs guttering.
• Blank run fields are treated as zero. You only need one valid run length to get a result.
• Waste allowance defaults to 5% if you do not enter a value. This is a simple buffer for cutting and minor measuring error, not a full design margin.
• Standard section length defaults to 3 m (meters mode) or 10 ft (feet mode) if you do not enter a value. Your supplier may use different lengths, so change this if needed.
• Results assume straight length purchasing only. Corners, miters, overlaps, and fitting losses vary by system and are not modeled here.

Common questions

Do I measure the building perimeter or the roof edge?

Measure the roof edge where the gutter will sit, not the footprint perimeter. Roof geometry can change the edge length, and many roofs do not use gutters on every side. If you are unsure, walk the eaves line (or measure from plans) and break it into straight runs you can enter separately.

What if I only have a rough estimate?

Use the best number you have and keep the waste allowance at 5% or increase it slightly if your measuring method is rough. The calculator will still give a usable purchase quantity because it rounds up to whole sections. The main risk with rough inputs is underestimating one edge and buying one section too few.

Why does the calculator show “extra” length after rounding up?

Gutters are bought in fixed section lengths, so the total you buy must be at least your required length. The “extra” is the difference between the total length of the sections you purchase and your required length including waste. That extra may become offcuts or can be useful for small returns and adjustments, depending on the installation.

Should I increase the waste allowance for corners and fittings?

Not for most standard installations. Corners and fittings change the parts list more than the total straight length, unless your system requires significant overlap or you expect many cuts. If your layout has lots of short pieces and many joins, increasing waste from 5% to 8–10% can be a reasonable practical buffer.

Does this include downspouts and accessories?

No. This page is intentionally focused on gutter length and the number of gutter sections to buy. Downspouts, brackets, outlets, end caps, angles, sealant, and screws depend on local rainfall design, roof area, gutter profile, and manufacturer spacing rules. Treat this calculator as the “how much guttering” number only.