Before and After: Testing an Extender Spot Before You Buy One

An extender is a small purchase and a real gamble. You buy it, plug it in, move it three times, and only then find out whether the back bedroom was ever fixable from an outlet. The before-and-after comparison moves that test onto the floor plan, where a wrong answer costs nothing but a minute.

Here is how to read the two numbers it gives you, what size of improvement is genuinely worth paying for, and how to check three candidate outlets in about a minute.

What the comparison is actually comparing#

Two runs of the same simulation over the same plan. The Before map has your router and nothing else. The After map has your router plus an extender on the exact tile you picked. Same walls, same materials, same router position — the only thing that changed is the second radio.

That is why the pair is worth more than either map on its own. A single heatmap tells you the back bedroom is orange. The pair tells you whether the outlet in the hallway would do anything about it.

Both halves are predictions. Nothing here comes off your live network — the app does no scanning and runs no speed test — so what you are reading is the arithmetic of the geometry you described, square by square. What the colors mean is covered in what each band on the heatmap stands for; this article is about the numbers underneath them.

The two numbers on the results card#

The Results screen puts a Before/After toggle over the map and two summary tiles above it.

Coverage reads something like 62% → 81%, with +31% underneath. Coverage is the share of open floor at or above -67 dBm, the same threshold the app uses to count a square as weak. Notice what the trailing figure is doing: 62 to 81 is nineteen percentage points, but it is shown as a relative improvement of 31%. Both are true. Only one of them is the size of your problem.

Target room reads something like -78 → -63 dBm, with +15 dB underneath. That is the predicted level at the single tile you marked as the location you want to improve, before and after. Skip the target step and this tile does not appear at all, which leaves you judging a placement on coverage alone.

There is also a count of weak squares recovered. Treat it as texture, not evidence — it counts floor area, and floor area is not where you sit.

What counts as a meaningful improvement#

Decibels are logarithmic: 3 dB is double the power, 10 dB is ten times it. So the numbers look smaller than the changes they describe, and you need a yardstick. Use the map's own: one color band is roughly 5 to 8 dB, about the cost of one interior wall with wiring and plumbing in it.

Then apply the rule that overrides the entire table: the after value matters more than the size of the gain.

A target that moves from -85 to -71 dBm is a +14 dB improvement and still a room where video calls break up. A target that moves from -70 to -58 dBm is a smaller +12 dB and a room that now works properly. Set the bar by what happens in that room: -67 dBm is the practical floor for reliable video and voice, and -56 to -60 dBm is the comfortable target if the room also carries 4K or large uploads.

Check the backhaul before you believe the After map#

The simulation will happily draw strong signal around an extender that is starving. Before accepting any result, flip back to Before and look at the color of the tile the extender is standing on.

That tile wants to be green or yellow — roughly -60 to -67 dBm from the router. This is the extender's own link home, and everything it rebroadcasts is capped by it. If the tile is orange or worse, the After map is honest about signal strength and misleading about usable speed, because a repeater cannot publish quality it never received. The reasoning behind that window is in the halfway rule and the outlet it points to.

The second thing no coverage map shows is the throughput tax. On a single-radio extender, every packet crosses the air twice on the same channel, so devices behind it typically see around half the throughput the same signal level would give them straight from the router. For an HD video call at 1.5 to 3 Mbps each way, that is irrelevant. For a 4K stream at 15 to 25 Mbps sustained, or a camera uploading all day, it is the whole question.

Three candidate outlets in about a minute#

Real homes offer two or three plausible outlets, not hundreds. Testing all of them takes a few taps each.

1. Mark the target first. On the target step, tap the canvas in the room that made you search — the desk, the couch, the bed. Without it there is no target-room number to compare.
2. Write your candidates down as real outlets. The hallway wall, the stair landing, the outlet by the dining room door. Only places you can genuinely plug something in.
3. Place the extender on candidate A and open Results. Note both lines: the target pair, and the coverage pair.
4. Tap Try Another Spot, move the extender to candidate B, and read the same two lines. Then do C.
5. Rank by the after value, not the delta. The highest after number at your target wins, even if its improvement figure is smaller.
6. Break ties on the backhaul. Whichever candidate tile shows the stronger color on the Before map is the safer of two otherwise equal winners.
7. Then let the app search on its own and see whether it beats all three. Its sweep is not limited to the outlets you happened to think of, so it often returns a tile one room closer to the router than any of your candidates — the position you dismissed for being too near the router usually wins on backhaul.

Roughly twenty seconds per candidate, and the only thing you have spent is attention.

When the comparison tells you not to buy#

This is the outcome the exercise is really for, and it turns up in three recognizable shapes.

The best position gains less than 10 dB, or leaves the target below -67 dBm. Placement is not your constraint. Move the router first — getting the router out of the corner is free, and the swing available there is often bigger than anything an extender can add — then run the comparison again from the new baseline.

Nothing between the router and the problem room is better than orange on the Before map. There is nowhere for a repeater to stand. Every position with reach into the room has no link home, and every position with a link home has no reach. That is the signature of a problem that needs a wire rather than a radio, and MoCA or one Ethernet run ends it permanently.

The target improves nicely but the room needs sustained throughput. A home office pushing large uploads, a 4K TV, a security camera: the halving tax lands squarely on those, and a good dB number does not repeal it.

None of these are failures of the exercise. Finding out for free that the answer is "not this" is the entire reason to run it before the box arrives.

Running it on your own plan#

Sketch your layout or load one of the starter layouts, set the material preset to match what your walls are made of, drop the router where it truly sits, and mark the room you care about. Place a candidate extender, open Results, and toggle between Before and After. If the target moves two bands and lands at -60 dBm or stronger, the purchase is justified and you know which outlet to use. If it moves half a band, you just saved the hardware and an evening of moving it around the house. The placement rules behind all of this are collected in the extender placement guide, and you can get the app here.