Gutter tools

Linear footage. Measure every eave that will carry gutter. This is the divisor for every quote you receive.

Sizing. This Old House's method uses drainage area, a roof pitch factor from about 1.0 (flat) to 1.3 (12-in-12), and local rainfall intensity in inches per hour. Five-inch K-style covers roughly 5,520 square feet of drainage area; 6-inch about 7,960.

Downspouts. Roughly one square inch of downspout cross-section per 100 square feet of roof. A 2x3 handles about 600 square feet, a 3x4 about 1,200, a 3-inch round about 706 and a 4-inch round about 1,255.

Guard break-even. Guard quote divided by annual cleaning spend equals payback in years. With guards at about $40 per linear foot and cleaning at $191-$529 per visit, this calculation kills a lot of guard sales on its own — which is exactly why you should run it before the sales visit, not during.

How to choose

Measure before you call anyone

Knowing your footage changes how quotes are presented to you.

Treat calculators as sanity checks

They tell you whether a quote is in the right universe, not what your exact job costs.

Use local rainfall intensity

Sizing that ignores your regional rainfall rate will under-size in storm-prone areas.

Run the break-even before the pitch

Deciding in advance is the single most effective defense against a high-pressure close.

Recheck downspout count

It is the cheapest capacity fix and the most commonly skimped item on a bid.