Sprinter vs Transit vs ProMaster: interior dimensions for a conversion

Most Sprinter-vs-Transit-vs-ProMaster articles are driving reviews: engines, drivetrains, dealer networks, resale. All of it matters less than three interior numbers — cargo floor length, width between the wheel arches, and standing height — because those three decide which layouts are physically possible in each van. You can live with a drivetrain you didn't prefer. You cannot live with a bed that doesn't fit. So this is the comparison as a layout problem, not a road test.

The three numbers, per van

Approximate figures for the high-roof cargo variants converters actually buy. Published specs vary by model year and measurement point, so treat these as planning numbers and verify against the van in front of you before cutting plywood:

Three things jump out. The ProMaster is the widest — both between the arches and, more importantly, between the finished walls, roughly 1.87 m (≈73.5 in) at its widest point. The Transit high roof is the tallest inside by a clear margin. And the Sprinter 170″ has the longest floor of any van in the class. Each of those facts creates a layout, and each is worth a section.

Width: the ProMaster's entire argument

The bed is the biggest single object in a camper, and its orientation is the biggest single layout decision. A transverse (east–west) bed across the van frees roughly 1.9 m (≈6 ft) of floor length compared with a longitudinal (north–south) bed — that reclaimed length is your shower cubicle, your dinette, or your ability to buy the shorter, cheaper van in the first place.

Whether a transverse bed works comes down to one question: is the van wide enough at mattress height for you to sleep across it? In the ProMaster — at ~1.87 m between the walls before insulation — most people up to about 6 ft sleep east–west with modest wall trimming or none at all. This is no accident: the ProMaster is the North American twin of the Fiat Ducato, the box-shaped, front-wheel-drive van that dominates European conversions precisely because of this width. (If you're reading from Europe, the Ducato L2/L3/L4 layout guide covers the same body in its European lengths.)

The Sprinter and Transit are narrower — figure ~1.78 m (≈70 in) wall to wall before insulation, less after. A transverse bed in either means one of three compromises: sleeping diagonally, being short enough not to care, or cutting wall “flares” into the sheet metal to buy back 10–13 cm (≈4–5 in) per side. Flares work, but they are a real fabrication job on a brand new vehicle. The common alternative is a longitudinal bed — which then consumes ~1.9 m of floor length and pushes you toward the longer (and pricier) variant to fit everything else.

Front-wheel drive gives the ProMaster a second quiet advantage: no driveshaft under the floor, so the load floor sits lower. That means an easier step in, more usable garage height under a fixed bed, and more headroom margin for a raised shower tray.

Height: the Transit high roof stands alone

At ~2.05 m (≈6′9″) inside, the Transit high roof is the only van of the three where a 6′2″ person stands straight after floor and ceiling build-out — insulation, subfloor, and finish typically cost 7–10 cm (≈3–4 in) of the raw figure. The Sprinter high roof and ProMaster high roof both land around 1.93 m raw, which finishes out to comfortable standing for people up to roughly 6 ft and a permanent slouch above that.

Height also decides whether bunk-over-garage layouts breathe: a fixed bed at 1.05 m (≈41 in) to clear two bikes underneath leaves sitting headroom above the mattress in a Transit HR, and rather less in the other two. If you are tall, the Transit high roof is not a preference — it is the shortlist.

Length: the 170″ Sprinter is the full-timer spec

The Sprinter 170″ carries ~4.41 m of cargo floor — about 75 cm (≈2.5 ft) more than a ProMaster 159″ and nearly a metre more than a Transit LWB. That is the length class where everything fits at once: longitudinal fixed bed, separate shower cubicle, four-person dinette, and a garage — the spec you see on full-time rigs, because it is the only footprint here that doesn't force a trade. The cost is a van over 7 m (≈24 ft) bumper to bumper, which turns every parking decision into planning. The general length trade-off — what each extra 40–60 cm of floor buys and costs — is the subject of the LWB vs MWB guide; it applies to all three marques equally.

What the spec sheet hides

Four caveats before you take the table above as gospel. First, every figure is raw sheet metal. Insulation, furring, and wall panels take 4–8 cm (≈1.5–3 in) per side; floor build-up takes 4–5 cm more. The “fits by two inches” layout on paper does not fit in the finished van.

Second, width is not one number. All three vans taper as the walls rise, and they taper differently — the ProMaster's near-vertical, boxy walls (another Ducato inheritance) mean it keeps most of its width at mattress height, while the Sprinter's more rounded body loses width exactly where a transverse sleeper's shoulders go. Width between the arches matters for a different reason: it sets the widest continuous object — water tank, garage drawer, under-bed bike slot — you can place at floor level between the axles without building over the arch boxes.

Third, cargo length is measured at the floor. At counter height the usable run is shorter, because the bulkhead area slopes back over the cab seats — relevant the moment you plan a kitchen along the wall right behind the driver. And fourth, door openings constrain layouts too: whatever module sits opposite the sliding door has to leave a walkable entry, and a shower cubicle or wardrobe usually cannot.

None of this changes the ranking. It changes the margins — and marginal layouts are the ones that die between the sketch and the build.

The feasibility matrix

The honest version of this article is one table. “Tight” means it assembles with compromises — shorter bed, galley kitchen, convertible furniture. Assume a couple, average heights, high roof throughout:

*Tight in the narrow vans means diagonal sleeping, a sub-6 ft occupant, or wall flares. The ProMaster earns its two easy “Yes” cells in the bed row purely on body width — and note how that transverse bed then unlocks the shower row in a van with a shorter floor.

Read the columns, not the rows, and the marketing fog clears. The ProMaster 159″ delivers the couple-with-shower layout on a shorter, cheaper, lower-floored van than either rival — as long as nobody aboard is much over 6 ft. The Transit LWB-EL gets close to everything if the transverse bed question breaks your way or you accept longitudinal. The Sprinter 144″, the best-selling conversion base in the US, is genuinely the most constrained floor plan of the six — you are paying for the badge and the drivetrain, not for layout freedom. And the 170″ answers every row by brute force.

Payload: not the tiebreaker people expect

Weight capacity rarely separates these three. All of them offer variants with roughly 3,000–4,000+ lb (≈1,400–1,800+ kg) of payload, which is enough margin for a full couple's build with water, batteries, and gear — if you pick the right GVWR variant and actually run the numbers. A finished conversion routinely adds 1,500–2,500 lb before passengers, so the arithmetic is worth doing before the build, not at the weighbridge after it. The payload and weight guide walks through the component-by-component math; it applies identically to all three vans.

Settle it with the actual layout, not the forum

Every dimension above is a proxy for one question: does your layout fit? The fastest way to answer it is not another spec sheet — it is dropping your actual furniture into all three interiors and watching where it collides. VanPlot has the Sprinter, Transit, and ProMaster (and their European siblings) with true interior shells — wheel arches, wall curvature, real standing heights — free in the browser, with live payload and axle-load readouts as you place each piece. Build your layout once, swap the van under it three times, and the matrix above stops being our opinion and becomes your measurement.

Ten minutes in VanPlot before the test drives, and you'll walk into the dealership knowing exactly which van your build fits — and which rows of that table you personally can ignore.