Where the water lands matters most
In a heavy rain a downspout carries a steady stream. Let it out at the base of the wall and it soaks down beside the foundation, where it turns up as a damp basement, a wet crawlspace or soil washed out from under a walkway.
The estimate puts a splash block at each outlet, $32 to $72 for the set. A splash block spreads the stream and carries it a foot or two out, which is enough where the ground already falls away from the house. Concrete blocks stay where they are put; plastic ones are lighter and tend to get moved by mowers.
Where the lot is flat or the basement is already damp, the water needs to go further: a hinged extension that flips up for mowing, a roll-out sleeve that unfurls when water runs, or solid pipe buried to a pop-up emitter in the lawn or to daylight down the slope. None of those is in this estimate, and a buried line is a digging job priced on its own. Check before tying into any municipal pipe, because many cities forbid connecting downspouts to the sanitary sewer.
Extensions only help if the ground beyond them slopes away. Soil that has settled into a trough against the foundation sends water back to the wall whatever the downspout does.
2 by 3 or 3 by 4?
Residential downspouts come in two common rectangular sizes, 2 by 3 inches and 3 by 4 inches. The larger has twice the cross-section, 12 sq in against 6, so it carries much more water and passes the leaves and twigs that lodge in the elbows of the smaller one.
The 2 by 3 is common on older houses with 5-inch gutters and small roof sections. The 3 by 4 is the usual partner for 6-inch gutters, and many installers fit it to 5-inch gutters too, under trees or below a large or steep roof. Round downspouts go with half-round gutters.
Upsizing on existing gutters means cutting larger outlet holes, and the bigger pipe, elbows and straps all cost more, so ask which size a quote is for. This estimate prices aluminum. Galvanized steel stands up better to knocks from ladders and mowers, and copper costs far more than either.
How many, and where on the house
The common rule is one downspout per 30 to 40 feet of gutter. A longer run usually gets one at each end, with the gutter pitched down from the middle toward both. A roof valley pours a lot of water into a short length of gutter, so a downspout close to where it lands helps that gutter keep up in a downpour.
Corners are the usual spot: the pipe runs neatly down the corner trim and the outlet can be aimed along the side of the house toward lower ground. Keep outlets away from doors, paths and driveways, where the runoff freezes in winter. On a two-story house the upper gutter is often drained onto the lower roof, which wears the granules off the shingles beneath the outlet; piping it all the way down is kinder to the roof.
To use the calculator, measure from each gutter outlet to the ground, add a little for the offset at the top where the pipe steps back to the wall, and total the drops.
Reading the estimate, and a quote
The figure covers aluminum downspout in 10-foot sections, elbows, wall straps, splash blocks and fasteners, plus 8 person-hours at $65 an hour. That labor, $442 to $598, goes on planning the drop points, cutting and assembling each run with every upper piece slipped inside the one below so the joints shed water, strapping it at the top, middle and bottom, and flushing the gutters with a hose to check the flow.
It does not cover the gutters themselves, which you can price with the gutter cost calculator; new outlets cut into an existing gutter where there was no downspout before; removing old downspouts; and extensions or buried drains. Brick, stone and stucco take longer to fasten to than wood or vinyl siding.
Before signing, check that the paperwork gives the pipe size, the metal and color, how many drops and where, and what sits at the bottom of each one. If it stops at the wall, ask where the water goes next.