Undersizing a shade motor is the most common and most expensive mistake in a motorization project. The motor stalls, overheats, or simply refuses to lift a fully-loaded tube, and the only fix is a new motor. Sizing correctly takes three numbers: the torque the shade demands, the tube it has to fit inside, and the speed you can live with.
Once you know the torque and tube size you need, you can filter the full range of Somfy motors by family and control type.
1. Work out the torque the shade needs
Torque is rotational force, measured in newton-meters (Nm). The torque a roller shade demands rises with two things: the weight of the fabric assembly, and the radius of the roll it is winding onto.
That second factor is the one people miss. A shade winding onto a 2 in tube needs roughly a quarter more torque than the same fabric on a 1.5 in tube, because the motor is working at a longer lever arm. As fabric layers build on the tube, the effective radius grows through the travel, so peak demand is at the bottom of the shade, fully unrolled, at the moment it starts to lift.
Practical guidance for interior roller shades:
- Small shades up to about 40 in wide in standard solar fabric: 2 to 4 Nm. The Sonesse 28, 30 and 40 sizes live here.
- Typical residential shades, 40 to 80 in wide: 6 Nm covers most of this range. This is the busiest size in the catalog, the 506S2 and 506A2 motors.
- Wide or heavy shades, blackout fabric, dual-roller, or anything over 80 in: 10 Nm and up. 510S2, 515S2 and larger.
Exterior work is a different scale entirely, because wind load and fabric weight both climb. Cassette awnings and zip screens typically start at 25 Nm and run to 50 Nm or beyond, covered in the exterior motor range. Rolling shutters on 60mm tube can need 80 or 100 Nm.
If a shade sits near a boundary, size up. The cost difference between a 6 Nm and a 10 Nm motor is small next to the cost of replacing an undersized one.
2. Check the motor physically fits the tube
Torque is necessary but not sufficient. The motor also has to go inside the tube, and every Somfy motor states a minimum inside diameter that is a hard limit.
- Sonesse 28 and R28: from roughly 1.13 in (28mm) tube
- Sonesse 30: 1.13 in, the smallest practical size for a discreet interior shade
- Sonesse 40 / LS40 / LT40: 1.46 in (37mm)
- Sonesse 50 / LT50 (the 500 series): 1.85 in (47mm), which covers the 2 in and 2.5 in tubes that dominate residential work
- LT60 (600 series): 60mm tube, for rolling shutters and large exterior assemblies
Wall thickness matters as well as diameter. A tube with a thick wall or an internal profile has less usable bore than its nominal outside diameter suggests, and a crown that fits a 2 in round tube will not fit a 2 in profiled tube. Every listing on this site names the tube it fits.
3. Decide how fast it should move
Speed is measured in rpm and trades directly against torque within a motor family. Across the Somfy range, faster motors carry less torque and slower motors carry more:
- 30 to 38 rpm: fast, for light interior shades where you want the shade down quickly
- 20 to 25 rpm: the middle ground, and the most common choice for interior work
- 12 to 14 rpm: slow and strong, for heavy exterior assemblies and large rolling shutters
On a very tall shade, a fast motor is worth having. On a bank of shades that should move together, matching speeds matters more than absolute speed, because mismatched motors finish at visibly different times.
4. Do not forget noise
For bedrooms, media rooms and conference rooms, noise is a specification, not a preference. Standard Sonesse motors sit in the mid-40s. The Sonesse ULTRA range drops into the mid-to-high 30s, which is the difference between a shade you hear and a shade you notice only because the light changed.
Decibels are logarithmic, so the gap is wider than the numbers look. A 35 dB motor is not 22 percent quieter than a 45 dB one; it is roughly half as loud to the ear.
Verified figures for the common sizes
Rough bands are useful for planning. When you are about to order, use the published figure for the exact part number. Every row here comes from Somfy's own product record, linked below the table.
| Motor | Part | Torque | Speed | Noise |
|---|---|---|---|---|
| Sonesse 28 WireFree Zigbee | 1241755 | 1.1 Nm | 20 rpm | 44 dB |
| Sonesse 30 RTS 24V DC | 1241142 | 2 Nm | 25 rpm | 47 dB |
| Sonesse 40 RTS 404S2 | 1240380 | 4 Nm | 36 rpm | 42 dB |
| Sonesse 50 506S2 RTS | 1001809 | 6 Nm | 32 rpm | 45.1 dB |
| Sonesse 50 510S2 RTS | 1001807 | 10 Nm | 32 rpm | 47.2 dB |
| Sonesse ULTRA 50 504A8 DC RTS | 1134023 | 4 Nm | 25 rpm | 35 dB |
| Sonesse ULTRA 50 506A2 RTS | 1002562 | 6 Nm | 24 rpm | 38 dB |
Sources: Somfy's published product records for 1241755, 1241142, 1240380, 1001809, 1001807, 1134023 and 1002562. Full torque and tube tables for the range are in Somfy's 500 Series Databook.
Two things the table makes obvious. Torque and speed move against each other inside a family, and ULTRA buys roughly ten decibels for a few rpm. If you are choosing between sizes rather than within one, our Sonesse 28 vs 30 vs 40 vs 50 comparison sets them side by side.
Putting it together
Size the torque from fabric weight and tube radius, confirm the motor fits the tube's inside diameter, pick a speed band, and add the ULTRA premium where quiet matters. Then match the crown, drive and bracket to the tube, and choose the control protocol.
One trap worth naming: head type. Star and square heads take different brackets, and the Sonesse ULTRA 50 DC motors use a square head. Check it on the listing before you order the bracket.
Every product listing on this site carries Somfy-verified torque, speed, noise rating and minimum tube diameter, plus links to the official Somfy spec sheet. If you know the part number, searching it will take you straight there.
