Gutter Calculator

Use Gutter Calculator

Figures update as you type. Nothing you enter leaves this tab, and no values are stored.

Total eaves length (ft)Downspout every (ft)

Keep a run-by-run drawing beside this estimate. A total length can hide disconnected edges, and an arithmetic outlet count does not establish hydraulic capacity.

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About Gutter Calculator

Use this calculator to plan gutter runs and an initial downspout count, not to size a drainage system. Enter the roof edges that actually need gutters, rather than the building perimeter or sloping roof area. The length result matches your eaves measurement. The count divides that length by your chosen spacing, rounds up, and returns at least one downspout. Roof area, rainfall intensity, gutter profile and outlet capacity are not inputs, so this result cannot establish whether a system will handle heavy rain.

Using Gutter Calculator

Measure each gutter run in feet and add the lengths. Keep a separate sketch of corners, breaks and discharge points.
Enter the sum in Total eaves length. Enter your planned interval in Downspout every; both fields use feet.
Read the rounded-up downspout count, then check its placement against the individual runs. Separate runs may each need an outlet.
List brackets, corners, joiners, end caps and outlets separately before ordering. The calculator does not count these fittings.

Where gutter calculator helps

One 120-foot run

With 120 ft of eaves and a 35 ft interval, 120 / 35 is about 3.43. Rounding up gives four downspouts and 120 ft of gutter, before fittings or cutting allowances.

Three separate roof edges

Three disconnected 20 ft runs total 60 ft. A 35 ft interval gives two downspouts in the combined calculation, but each isolated run may need its own outlet. Calculate runs separately and review the layout.

Before you use the result

Spacing is a planning assumption, not a drainage standard. Confirm system capacity and outlet positions with the product specifications and a qualified installer.
The displayed gutter length is rounded to whole feet. Keep your original measurements for ordering, cutting and deciding section lengths.
Zero eaves still returns a minimum count of one in this estimator. If no gutter run is needed, do not interpret that minimum as an installation requirement.

Questions about Gutter Calculator

Does this calculate gutter diameter or rainfall capacity?

No. It uses length and spacing only. It does not model roof catchment area, rainfall, slope, gutter diameter or restrictions at bends and outlets.

Should I add a fixed waste percentage?

Not automatically. Compare each measured run with available stock lengths and the joining method. Offcuts from one run may be usable on another; fittings and joint overlaps also affect the order.