Gutter guides
A good gutter project is decided by three numbers: your linear footage, your drainage area, and your local rainfall intensity. Get those right and the rest - material, guards, brand - is comparison shopping. Get them wrong and no product will stop the overflow.
Sizing. This Old House's method combines three factors: the roof drainage area feeding each gutter section, a pitch factor (about 1.0 for a flat roof up to 1.3 for a 12-in-12), and your regional peak rainfall intensity in inches per hour. A 5-inch K-style gutter covers roughly 5,520 square feet of drainage area; 6-inch takes it to about 7,960.
Downspouts. The rule of thumb is about one square inch of downspout cross-section per 100 square feet of roof. A 2x3 rectangular downspout serves roughly 600 square feet, a 3x4 about 1,200, a 3-inch round about 706 and a 4-inch round about 1,255. Chronic overflow at one corner is very often a downspout count problem.
Measuring. Walk the perimeter and measure every eave that will carry a gutter. That is your linear footage, and it is the number every quote should be divided by.
Hiring. Give every bidder the same written scope: footage, material and gauge, gutter size, profile, number and size of downspouts, discharge locations, any fascia repair, guard type if any, and haul-away. Confirm licensing and insurance through your state or local licensing authority - requirements differ by state and by city, so check your own jurisdiction rather than trusting a contractor's summary of the rules.
Choosing gutters an approach
The judgement calls that decide the bill, before anyone quotes you.
- Start with drainage area, not price An undersized system installed beautifully still overflows every storm.
- Count downspouts deliberately Adding a downspout is one of the cheapest capacity upgrades available.
- Standardize the scope before bidding Identical written scope to every bidder is the only way to compare prices honestly.
- Verify insurance with the carrier Ask for the certificate and call the insurer. Ladder work on your property is a real liability question.
- Ask where the water goes Discharge placement is part of the design. Dumping into a splash block next to the foundation is not a plan.
- Get the payment schedule in writing Large up-front deposits on a one-day job are a warning sign.
All gutters guides
Gutter Sizing Guide
How Gutters Protect Foundation
Gutter Guard Buying Guide
Gutter Maintenance Calendar
Where these figures come from
Sources last checked
- This Old House - How To Size Gutters and Downspouts · retrieved 2026-07-25
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