Marble Window Sill and Threshold Cost in 2026: Price Per Linear Foot
A marble window sill is a small piece of stone and a disproportionately confusing line item on a quote. Fabricators don’t price it by the square foot the way they price a countertop — a sill barely covers a square foot to begin with — they price it per linear foot, per piece, or as a flat “sill charge” that bundles material, cutting, polishing and setting into one number that’s hard to compare across bids. Thresholds get the same treatment. The result is that homeowners doing a full renovation — eight window sills, three door thresholds, a shower curb — often have no idea whether $65/linear foot is a fair number until they’ve already signed.
This guide prices window sills and thresholds by stone and by piece type, walks through what actually drives the linear-foot number up (it’s not the stone, mostly), and works a real house budget line by line. Every dollar figure is a market estimate for August 2026, built from the slab prices in our price index plus standard US fabrication and setting rates — never an invented number. Factory-direct cut-to-size sourcing typically runs 30–60% below a Western fabricator’s installed price for the same piece; the honest trade-off is freight, duty and an 8–10 week lead time, covered below. Nothing here is a quote — get one for a specific project at /quote/.
What “sill” and “threshold” actually mean
The two words get used loosely, and a quote that doesn’t specify which piece it’s pricing is a quote you can’t check. Five distinct pieces show up under this heading:
| Piece | Typical depth | Typical thickness | Typical length | Finished edges |
|---|---|---|---|---|
| Interior window sill (stool) | 4–6“ | 3/4“–1“ | window width + 2–4“ “horns” each side | Front face + 2 ends polished; horns mitred or returned |
| Exterior window sill | 5–8“, sloped top (“wash”) | 1“–2“ | window width + 1–3“ overhang | Front, both ends, sloped top, drip groove underneath |
| Interior door threshold (saddle) | 4–6“ | 3/4“–1“ | door width, usually 32–36“ | Both long edges bevelled, ends square-cut |
| Shower threshold / curb | 4–6“ flat, or a 4–5“-tall curb | 3/4“–1.25“ | shower opening width, 24–42“ | Top pitched toward the drain, edges eased |
| Exterior door threshold / saddle | 5–7“ | 1“–1.5“ | door width | Top sloped, weep groove cut underneath, ends returned |
Exterior sills need the sloped top and drip groove for one reason: water. A flat exterior sill pools rainwater against the window frame and rots it from below; the wash sheds water outward and the groove stops it wicking back under the sill by capillary action. Interior sills and thresholds skip both details, which is one reason interior pieces are cheaper to cut even before you get to stone choice.
Price per linear foot, by stone
The number below is built the same way every product-category estimate on this site is built: the stone’s slab price from our index, applied to a standard 6“ (0.5 ft) sill depth, plus the fabrication and setting costs a US shop typically charges for a small, three-edge-polished piece. Small pieces carry a much higher labor-to-material ratio than a countertop slab — a fabricator still has to template, cut, polish and often mitre the horns on a piece that might only use $10 of stone — so fabrication is usually the bigger half of the number, not the material.
| Stone | Slab price (index, $/sqft) | Material, 6“ depth | Fabrication (cut, 3-edge polish, horns) | Setting/install | Installed, per linear ft |
|---|---|---|---|---|---|
| Guangxi White marble | $15–35 | $7.50–17.50 | $20–35 | $8–15 | $35–70 |
| Carrara marble | $40–90 | $20–45 | $20–35 | $8–15 | $50–95 |
| Black Marble | $30–80 | $15–40 | $20–35 | $8–15 | $45–90 |
| Calacatta marble | $80–250 | $40–125 | $25–45 | $8–15 | $75–185 |
| Travertine (interior only — see below) | $8–40 | $4–20 | $18–30 | $8–15 | $30–65 |
| White Granite (exterior-rated) | $35–90 | $17.50–45 | $25–45 | $10–18 | $55–110 |
| Absolute Black Granite (exterior-rated) | $30–75 | $15–37.50 | $25–45 | $10–18 | $50–100 |
Two things jump out. First, Guangxi White at $35–70/linear ft and Carrara at $50–95/linear ft aren’t that far apart even though the slab price nearly triples — because fabrication and setting are flat costs that don’t scale with stone grade, they compress the gap between a budget and a mid-tier stone once you’re pricing a 3–4 ft piece rather than a 45 sqft countertop. Second, Calacatta is the only stone here where material cost, not fabrication, is the majority of the number — at the top of its range a single 4 ft sill can use $500 of slab before a single cut is made, because a fabricator won’t chase a narrow sill shape out of a full Calacatta slab and waste the rest; they price in the offcut.
Travertine is listed for interior sills only. It’s porous and pits, which is exactly the character that makes it popular for floors and pool decks (see our travertine vs marble flooring comparison), but an exterior sill sits in standing water and freeze-thaw cycles more than almost any other piece of stone in a house — unfilled travertine there will spall within a few winters in a cold climate. For exterior sills and thresholds, granite is the standard swap: harder, denser, and far less porous, which is also why it dominates the outdoor kitchen category.
What actually drives the linear-foot number up
- Horns and returns. A window sill that extends past the window frame on both sides (the “horns”) needs those ends mitred or hand-returned rather than just cut square — that alone adds $10–20/linear ft over a sill cut flush to the frame, because the corner has to be shaped and polished on three sides instead of butted against drywall.
- The sloped wash on exterior pieces. Cutting an accurate slope and drip groove is a second setup on the saw and a slower polish pass than a flat interior sill — budget $10–25/linear ft more than the interior number for the same stone.
- Length under the minimum. Most shops have a per-piece minimum of $85–150 regardless of linear footage, because templating, saw setup and delivery cost the same whether the piece is 18“ or 4 ft. A single 2 ft bathroom window sill often prices at the minimum rather than at the linear-foot rate.
- Mitred returns at outside corners. A wraparound sill on a bay window, or a threshold that turns a corner, needs a mitred joint at the corner instead of a butt joint — add $40–80 per mitred corner, similar labor to the waterfall-edge mitre covered in our edge profile cost guide.
- Thickness. Interior sills are almost always 3/4“–1“; going to a full 1.25“–2“ slab (common on deep exterior sills for strength against point loads) roughly doubles material cost and adds saw time, the same relationship covered stone-by-stone in our slab sizes and thickness guide.
- Colour and vein matching across multiple pieces. A house with twelve window sills that all need to come from the same vein lot — so a Calacatta living room doesn’t visibly clash with the Calacatta sill next to it — pushes a fabricator toward buying one full slab up front rather than sourcing offcuts room by room, which raises the effective material cost per piece even though the linear-foot math looks the same.
Case study: a 1920s house renovation
A representative whole-house job: seven interior window sills (average 3.5 ft finished length including horns), one exterior door threshold (3.5 ft), two interior door thresholds (3 ft each), and one shower curb (3.5 ft). Interior pieces in Carrara, mid-band; exterior threshold in Absolute Black granite for durability. Market estimates, August 2026, US mid-range metro.
Local fabricator, supply and install:
| Line item | Math | Cost |
|---|---|---|
| 7 interior window sills, Carrara | 7 × 3.5 ft × $72/linear ft (mid-band) | $1,764 |
| 2 interior door thresholds, Carrara | 2 × 3 ft × $72/linear ft | $432 |
| 1 shower curb, Carrara, pitched top | 1 × 3.5 ft × ($72 + $15 slope premium) | $304.50 |
| 1 exterior door threshold, Absolute Black granite | 1 × 3.5 ft × $75/linear ft (mid-band) | $262.50 |
| Piece minimums (3 pieces fall under 3 ft length, bumped to $100 minimum) | 3 pieces, difference absorbed above | included |
| Delivery and site coordination | flat | $150 |
| Total | $2,913 |
Same specification, factory-direct cut-to-size from our partner mill:
Sills and thresholds are exactly the kind of piece our tiles category covers — “skirting, thresholds and stair treads cut from the same blocks for colour consistency” is a standard line item, priced by finished square footage rather than a linear-foot fabrication surcharge, because the mill’s labor cost is a fraction of a US shop’s.
| Line item | Math | Cost |
|---|---|---|
| 10 sills/thresholds in Carrara, ~0.5 sqft each finished (~5 sqft total) | 5 sqft × $30/sqft finished (factory cut-to-size, mid-band above the $18 base for the extra edge work) | $150 |
| 1 exterior threshold in Absolute Black granite, ~1.75 sqft finished | 1.75 sqft × $50/sqft finished | $87.50 |
| Ocean freight + duty share (small item riding with a larger container order) | flat estimate for a partial-container add-on | $180 |
| Local mason setting (mortar bed, shimming, caulk — same labor regardless of sourcing) | 10 pieces × $25 average | $250 |
| Total | $667.50 |
The factory-direct total lands about 77% below the local-fabricator number — a wider gap than the usual 30–60% factory-direct band, because sills and thresholds are almost pure labor arbitrage: the stone itself is a small fraction of either number, and it’s exactly the labor-heavy cutting and polishing step that costs far less at the mill. The catch is real, though: this order only makes sense bundled into a larger factory shipment (slabs, tiles or countertops for the same project), because a handful of sills alone won’t fill a container and the 8–10 week lead time means you’re ordering before demolition, not after you discover you’re short a sill. Renovations that only need window sills fixed after the fact are the case where local sourcing wins on time even while losing on price — see our fabricator selection guide for how to vet the shop doing that faster, pricier job.
Interior vs exterior: don’t cross-shop the stone
The single most common mistake on this line item is picking the interior stone (usually the same marble as the countertops, for a matched look) and specifying it for an exterior sill too, because “it’s the same house, it should match.” Exterior sills sit in direct weather — rain, freeze-thaw, UV, de-icing salt near a front step — and a soft, calcite-based marble like Carrara or Calacatta will etch, stain and eventually spall at the drip edge within a handful of seasons in a cold climate. It’s the same physical weakness covered in our marble vs granite comparison: marble’s low Mohs hardness and acid sensitivity are a non-issue on an interior stool that never sees rain, and a real problem on a piece that does. Absolute Black or a dense uniform granite (see our granite vs quartzite durability discussion for the same logic applied to a different pairing) is the standard swap for anything exterior, and the price difference — $50–110/linear ft vs $45–185/linear ft for interior marble grades — is close enough that durability, not cost, should decide it.
Installation: what the setting labor actually covers
The $8–18/linear ft setting cost in the tables above isn’t just “screw it in” — a sill or threshold is a small, visible, load-bearing piece and gets bedded properly or it cracks:
- Mortar or thinset bed, not just caulk, so the piece is fully supported along its length rather than resting on high spots that create a stress point under foot traffic (thresholds) or a closing window sash (sills).
- Shimming to level, checked with a level across the full length — a threshold that rocks even slightly will crack at the first heavy step.
- Perimeter caulk, flexible sealant rather than rigid mortar at the stone-to-frame joint, so seasonal wood movement doesn’t crack the stone.
- Sealing, for porous stones especially — a shower curb or exterior sill in a polished marble benefits from an impregnating sealer at install, the same product and schedule covered in our sealing guide.
Skipping any of these to save the $8–18/linear ft doesn’t remove the cost — it just moves it to a repair bill later, usually a cracked sill from an unsupported span.
FAQ
How much does a marble window sill cost per linear foot?
$35–185/linear foot installed, depending on stone. Budget white marble like Guangxi White runs $35–70/linear ft; Carrara runs $50–95/linear ft; Calacatta runs $75–185/linear ft. Figures are market estimates for August 2026, built from slab prices plus typical US fabrication and setting costs.
Why is a small sill so expensive per square foot compared to a countertop?
Fabrication and setting are largely flat costs — templating, cutting, three-edge polishing, horn returns and delivery cost close to the same whether the piece is 18 inches or 6 feet — so a small piece carries a much higher labor-to-material ratio than a large countertop slab. Most shops also apply a per-piece minimum of $85–150 regardless of length.
Can I use marble for an exterior window sill or threshold?
Not recommended in a cold or wet climate. Marble is soft and acid-sensitive, and an exterior sill sits in standing rainwater and freeze-thaw cycles that will etch, stain and eventually spall it at the drip edge within a few years. Granite (Absolute Black or a dense uniform grade) is the standard exterior swap at a similar or lower price point.
What’s the difference between a window sill and a window stool?
They’re the same interior piece in US usage — the flat, horizontal piece inside the window opening that the sash rests against, usually extending past the frame on both sides (“horns”). “Sill” sometimes refers specifically to the exterior sloped piece outside the frame; check which one a quote means before comparing prices.
Is factory-direct sourcing worth it for just a few window sills?
Usually only if it rides along with a larger order — slabs, tiles or countertops for the same project — because a handful of sills won’t fill a container on their own and the 8–10 week lead time means ordering before demolition starts. For a standalone repair or a small renovation without a bigger stone order, a local fabricator is faster even though it’s typically 3–4x the per-piece cost.
Do shower thresholds need a different cut than door thresholds?
Yes. A shower threshold’s top surface is pitched toward the drain rather than flat, and the stone needs to be non-porous or well-sealed since it sits in standing water daily — the same reasoning that rules marble out for exterior sills applies here, though honed marble sealed on a strict schedule is still common in dry climates. A door threshold is flat or has a minimal bevel and doesn’t need the pitch.