Ex-office mini PCs are the backbone of many homelabs. They're cheap on the used market, quiet, low-power, and small enough that five of them run a Proxmox cluster in less space than one tower. The two you see most are Lenovo's ThinkCentre Tiny (M720q, M920q, M70q, M80q, M90q and friends) and Dell's OptiPlex Micro. Physically they're nearly the same size. This guide compares them as rack occupants and covers how to mount each in 19-inch and 10-inch racks.

Side-by-side dimensions

Lenovo ThinkCentre Tiny: 179 × 34.5 × 183 mm (W × H × D)
Dell OptiPlex Micro: 182 × 36 × 178 mm (W × H × D)
One rack unit: 44.45 mm

Both are comfortably under 1U in height, with room for a floor or tray underneath. The Dell is 3 mm wider and 5 mm shorter in depth; the Lenovo is 1.5 mm lower. Exact sizes vary slightly by generation, so measure your own machine before ordering anything custom. Measure the case itself, not the rubber feet or a cable plugged into it.

How they differ as homelab boxes

Lenovo ThinkCentre Tiny

Some generations (notably the M720q and M920q) take a low-profile PCIe card with Lenovo's riser, which is why homelabbers prize them for 10 GbE or extra NICs.
Front power button and front USB; display, USB and Ethernet on the back.
External power brick. Plan where it lives.

Dell OptiPlex Micro

Very common in used corporate fleets, so they're easy to buy in matched sets.
Front power button; rear I/O with display outputs, USB and Ethernet.
Also uses an external power brick.

For racking, the practical difference is small. Both are front-to-back boxes with the power button at the front, which is exactly what you want in a rack. If you plan to add a PCIe card, check that the mount leaves the rear slot area open.

Option 1: 19-inch rack, 1U, one per mount

Both fit a 1U mount in a full-size rack. Our 19" Lenovo ThinkCentre Tiny 1U mount and 19" 1U Dell OptiPlex Micro mount are $38.99 each. They print as a centre tray plus two rack ears that bolt on with M4 bolts, with the nuts held in printed pockets. They come in PETG by default, or ASA for warm racks.

Option 2: 19-inch rack, two per 1U

A 19-inch rack has about 450 mm between the rails, so two Tiny or Micro PCs (about 360 mm together) fit side by side in one unit. Our catalog includes community designs such as the Lenovo Tiny PC 2× 1U mount and a Dell Micro PC 1U mount. Each is an open design licensed for commercial printing, with the designer credited on the page. Or set "Two devices side by side" in our generator to design a matched pair for either brand with a price in about 30 seconds.

Two per unit packs more machines into the rack, but airflow is tighter. Leave a vented blank above every second row if the rack is enclosed.

Option 3: 10-inch rack, 1U

A 10-inch rack has roughly 220 mm of usable width, and both machines (179 and 182 mm) fit in 1U with a little room to spare. That makes a desk-sized mini rack of four or five Tiny or Micro PCs a realistic project.

Lenovo: our 10" 1U Lenovo ThinkCentre Tiny mount is $30.99. There's also a community Tiny 10" mount with optional keystone sockets.
Dell: we don't have a ready-made 10-inch OptiPlex Micro listing right now. Enter 182 × 36 × 178 mm in the generator, choose 10-inch and 1U, and it will design and price one. 10" 1U mounts start from $30.99.

Heat and materials

Neither machine runs hot at idle, but a rack full of them under sustained load (a busy Proxmox node, a build server, a Plex transcode) warms the air around the mounts. PETG, our default, is fine in a normal room or a ventilated closet. For an enclosed cabinet, a mount that sits directly above another device, or a garage that gets hot in summer, choose ASA, which keeps its shape at higher temperatures. The materials guide lists the trade-offs. Whichever you choose, keep the front intake and the rear exhaust of each machine clear, and don't run a cable bundle across the rear vents.

Power bricks and cabling

Both machines use laptop-style bricks, and five bricks is a bigger cabling problem than five computers. A few approaches that work:

Strap bricks to a rear shelf or the back rails with hook-and-loop, out of the exhaust air.
In a 10-inch rack, a 1U IEC power distribution unit at the back keeps the AC side neat.
Run Ethernet to a keystone patch panel so you can move machines without re-running cable.

Printed vs metal

Metal 1U kits for these machines exist. At the time of writing, a branded steel Lenovo Tiny 1U kit lists around $139 MSRP, and Lenovo itself sells VESA and clamp brackets, not a rack kit. A printed mount at $30.99–$38.99 makes more sense when you're racking a stack of used machines that cost under $200 each. Our catalog parts carry a fit guarantee: send a photo within 30 days and we reprint free (terms).

Which should you buy?

If you need a PCIe slot, the Lenovo Tiny generations with riser support win. Otherwise, buy whichever you can get in a matched set at the best price, since they rack almost identically. Mixing brands is fine: one 19-inch rack can hold both on separate 1U mounts. For more small-machine racking, see “Mac mini M4 rack mount options” and the “10-inch rack starter guide”.

FAQ

Will a Lenovo Tiny mount fit a Dell OptiPlex Micro?

Not reliably. The Dell is 3 mm wider and 1.5 mm taller, which is enough to bind in a snug pocket. Use the mount sized for your machine, or generate one from your own measurements.

Do these fit in 1U in a 10-inch rack?

Yes. Both are 36 mm or less tall and about 180 mm wide, under the 1U height and within the roughly 220 mm usable width of a 10-inch rack.

Can I fit two side by side in a 10-inch rack?

No. Two need about 360 mm, which only works in a 19-inch rack.

Lenovo ThinkCentre Tiny vs Dell OptiPlex Micro for a homelab rack