Where to put a 4G or 5G router for the best signal

A 4G or 5G router (a "box" in France) can be a good alternative to a slow fixed line, but only if it gets a decent signal. Moving it a couple of metres can change speeds by a factor of two or three. Here is a method that works better than walking around watching the bars.

Step 1: find your carrier's mast and its direction

Look up your address on the map and find the nearest mast for your router's carrier, not just the nearest mast. Note two numbers from the table: the distance and the compass direction (for example "1.2 km, south-west").

Then look at the generations listed for that mast. If it carries 5G and your router is 5G, you will want it facing that mast. If the closest 5G mast is much further away than the closest 4G mast, a 4G connection to the near mast can be faster than a weak 5G one.

The nearest mast is not always the best. A slightly further mast with a clear line of sight often beats a closer one hidden behind a hill or a large building. Check the second and third masts in the same direction too.

Step 2: choose the room and the spot

Radio signals come into a building mostly through windows and through the walls facing the mast. Good spots share these features:

• On the side of the home facing the mast. A router on the opposite side has to receive through the whole building.
• Next to a window, ideally high up. Upstairs is usually better than downstairs, and a shelf better than the floor.
• Away from metal. Radiators, metal shutters, mirrors, fridges and foil-backed insulation block or reflect the signal.
• Watch out for coated glass. Modern energy-saving glazing often has a thin metallic coating that can weaken mobile signals noticeably. An old single-glazed window or a skylight can work better.

Step 3: measure with the right numbers

The bars on a router are coarse and every manufacturer draws them differently. Open the router's admin page (usually through a web address printed on its label, or its app) and look for these values:

SINR has the biggest effect on speed. A strong but noisy signal (high RSRP, low SINR) is slower than a moderate clean one. Our dBm signal calculator converts readings into plain-language quality levels.

Move the router between two or three candidate spots, wait a minute at each so the values settle, and note RSRP and SINR. Keep the best spot.

Step 4: test speed at different times

A cell is shared by everyone nearby. A speed test at 2 pm and another at 9 pm can give very different results, because evenings are busy. Test at least once in the evening before deciding a spot "works".

Step 5: lock a band if your router allows it

Some routers let you choose which frequency band to use. In France, low bands (700 and 800 MHz) travel further and pass walls better but carry less data; higher bands (1800, 2100, 2600 MHz and 3.5 GHz for 5G) are faster but need a clearer path. If your router keeps switching to a weak high band, locking a lower one can make the connection more stable, and the reverse when you are close to the mast. Our 5G by carrier guide lists which bands each French network uses.

When to give up and go outdoors

If the best spot indoors still shows RSRP below about -110 dBm or SINR around 0 dB, the building is the problem. An outdoor antenna aimed at the mast usually fixes it: see choosing and aiming an outdoor 4G/5G antenna.