A whole-house roof area cannot show which gutter run receives water from a valley, an upper roof, or a rear lanai. Before comparing Tampa Bay gutter estimates, divide the roof into named drainage zones and trace each zone all the way to the ground.
The arithmetic is useful for scale: one inch on 1,000 square feet is about 623 gallons. It is not a sizing formula. A proposal still has to address how quickly water arrives, where the roof concentrates it, which outlets serve the run, and where each downspout ends.
Build one row for every drainage zone
Use a name that will still make sense on an estimate or photograph: “front garage,” “west lower roof,” or “rear lanai valley.” Complete the same eight fields for each zone.
| Field | Record before the estimate | Resolve in writing |
|---|---|---|
| 1. Zone name | Plain property label and matching photo number | Which roof area and gutter run the proposal covers |
| 2. Horizontal dimensions | Plan-view length and depth feeding the run | Who verifies the field measurement |
| 3. Upper-roof contribution | Downspout or roof plane emptying onto a lower roof | Whether that added flow is included in review |
| 4. Concentrated flow | Valleys, inside corners, long runs, or adjacent roof intersections | How the proposal treats each concentration point |
| 5. Existing outlets | Outlet and downspout locations, restrictions, and visible overflow marks | Included outlets, downspouts, and changes |
| 6. Receiving surface | Soil, mulch, paving, slope, low spot, drain, or foundation-adjacent ground | Where the gutter scope ends and another review begins |
| 7. Visible evidence | Staining, splash marks, washed mulch, ponding, loose fasteners, or wet fascia | Observation, proposed work, and excluded diagnosis |
| 8. Proposal status | Each run, outlet, extension, removal, repair, and exclusion | Included, conditional, excluded, or not stated |
This organization comes from CamoKrew’s roof-runoff worksheet, a published first-party process source. Its useful contribution is the zone-by-zone field record. It does not establish that the company’s design, workmanship, credentials, or proposed solution is right for a particular property.
Calculate volume only as a comparison scenario
Use the horizontal plan area that drains to the zone—not the sloped surface area of the roofing:
horizontal area × rainfall depth × 0.623 = theoretical gallons
The coefficient appears in the EPA’s NEWR method record. The USGS gives a useful check: one inch on a 40-by-70-foot roof, or 2,800 square feet, is about 1,743 gallons (USGS rain-volume example). That works out to about 0.6225 gallon per square foot, consistent with 0.623 after rounding.
| Horizontal zone | 1 inch | 2 inches | 3 inches |
|---|---|---|---|
| 400 sq. ft. | 249 gal. | 498 gal. | 748 gal. |
| 800 sq. ft. | 498 gal. | 997 gal. | 1,495 gal. |
| 1,200 sq. ft. | 748 gal. | 1,495 gal. | 2,243 gal. |
These figures answer one narrow question: how the theoretical volume changes with area and depth. They do not answer how quickly the rain falls. Two inches delivered slowly and two inches delivered in a short downpour have the same total volume and different peak-flow demands.
Trace every outlet beyond the downspout
Do not stop the worksheet at “downspout included.” Photograph or sketch what happens next. Mark entrances, walkways, driveways, pool decks, planting beds, low spots, neighboring property, and ground close to the building.
Use three separate columns:
- the visible receiving condition;
- the gutter proposal’s included termination or extension; and
- any grading, underground drainage, easement, right-of-way, floodplain, or design question excluded from that proposal.
A longer extension or underground connection is not automatically suitable because it moves water farther. The receiving condition and responsible authority still need a property-specific answer.
Make two estimates comparable
Give every bidder the same zone sheet and photographs. Then compare each proposal against the same fields:
- named runs and profiles;
- outlets and downspouts by zone;
- extensions and final termination points;
- removal and disposal;
- fascia, soffit, roofing, screen-enclosure, or structural boundaries;
- underground-drainage and grading exclusions;
- permit or other-approval responsibility; and
- closeout evidence.
Do not fill a blank with an assumption. Mark it not stated and ask for a revision. Our separate guide explains why Hillsborough gutter and soffit repair scope must be defined before permit assumptions.
Source and method
Local Service Ledger reviewed the CamoKrew worksheet, USGS example, and EPA method on August 13, 2026. We reproduced nine volume scenarios and separated calculation inputs from the field and authority questions that the arithmetic cannot answer. We did not measure a roof, inspect drainage, size a component, review an estimate, or recommend a contractor.
Publication decision
This article is complete for editorial review but remains noindex and not approved for publication. A human must approve the source inclusion, relationship disclosure, structured business link, and final article before it can publish.