Damp meter reading checker
Your meter shows 24. Is that fine, or is that a problem? It depends entirely on what you pressed it against, and on whether the wall is wet or merely salty. Put your reading in and find out what it actually tells you.
Enter the figure your meter showed. On plaster or plasterboard a resistance meter reports % WME.
22% on plaster or plasterboard
Damp confirmed
Plaster begins to fail from here: blown patches, bubbling paint, salt bloom. Something is wetting this wall. The job now is finding out what, not treating the plaster.
This is a WME figure, not the moisture content of your wall. Resistance meters are calibrated on wood, so on plaster or masonry the reading tells you what the wood scale would show if this were wood. It is a useful comparative signal and it is not a measurement of how much water is in the material. Read the section on salts below before you act on a high number.
What this is based on
- Timber bands follow standard UK practice: 8% to 12% for internal timber in a heated home, a fungal decay risk emerging around 20% at which dry rot can establish, and rot well supported by sustained readings above roughly 24%.
- Masonry WME bands follow the surveyor rule of thumb of below 20% low, 20% to 27% moderate, above 27% high, and above 35% a genuine concern.
- Plaster is treated as more sensitive than the masonry behind it, with 12% to 15% dry and failure from about 20%.
- Resistance meters read moisture content directly on timber only. On every other material the figure is Wood Moisture Equivalent, and is comparative rather than absolute.
- The reference method for masonry remains gravimetric analysis of a drilled sample, as set out in BRE Digest 245. No surface meter replaces it, and the Property Care Association says as much.
Figures reviewed 17 August 2026.
Damp meter readings chart
There is no single threshold that means damp, because the same meter reads three materials on three different scales. This is the chart, and the numbers underneath it are the part that matters.
| Reading | Timber (%MC) | Plaster (%WME) | Masonry (%WME) |
|---|---|---|---|
| Dry | Up to 12% | Up to 15% | Up to 20% |
| Monitor | 12% to 16% | 16% to 20% | 20% to 27% |
| Damp | 16% to 20% | 20% to 27% | 27% to 35% |
| Serious | Above 20% | Above 27% | Above 35% |
Timber has the lowest thresholds and the most serious consequences, which is the opposite of what most people assume. A wall reading 25% is worth investigating. A joist end reading 25% is at real risk of rot if it stays there.
The thing nobody explains: WME
Almost every damp meter sold in the UK is a resistance meter. Two pins, a small current, and a measurement of how easily electricity crosses the gap between them. Wet materials conduct better than dry ones, so resistance is a decent proxy for moisture.
The catch is calibration. These meters were designed for the timber trade, and the scale was built by measuring the resistance of wood at known moisture contents. On wood, the number is real: 18% means the timber is 18% water by dry weight.
Press the same meter against plaster and the electronics have no idea it has changed material. It measures resistance and converts it using the wood curve. What you get is Wood Moisture Equivalent: the reading wood would give if wood conducted electricity the way this plaster does. It is not the moisture content of the plaster. It cannot be, because plaster and wood hold and conduct water completely differently.
This matters because a great deal of expensive remedial work gets sold on the back of a WME figure presented as if it were a moisture content. "Your wall is 30% wet" is not a statement the instrument is capable of making. What WME is genuinely good for is comparison: this wall against that wall, this month against last month, low down against high up. Used that way it is a legitimate and useful tool. Used as an absolute measure it is a sales prop.
When an absolute figure is needed, the method is gravimetric analysis: drill samples from the wall at different depths and heights, weigh them, dry them, weigh them again. BRE Digest 245 sets out how, and the Property Care Association is explicit that this, not a surface meter, is what determines moisture content in masonry.
Three things that make a dry wall read soaking
A high reading is not proof of water. Resistance meters measure conductivity, and several entirely dry things conduct beautifully.
1. Hygroscopic salts
This is the big one, and it is behind a large share of misdiagnosed rising damp. Where moisture has moved through masonry over years, it carries dissolved nitrate and chloride salts and deposits them as it evaporates at the surface. Those salts do two things. They conduct electricity directly, and they draw water out of the room air, so the plaster around them stays measurably damper than the air alone would explain.
The result is a wall that has been dry for a decade still reading 30% WME, with a contractor pointing at the meter. If you see white fluffy bloom, crystalline deposits or patches that go dark in humid weather and pale in dry weather, salts are in play. Fixing that is a replastering job with a salt-retardant system, not an injected damp-proof course.
2. Metal, foil and conductive backing
Foil-backed insulated plasterboard is now common on external walls, and it will take a pinless meter straight to the top of its scale on a completely dry wall. So will metal lath in older lath and plaster, plumbing runs, cables, nail heads and some metallic paints. A pinless meter cannot tell the difference between water and a sheet of aluminium. If your readings are uniformly maxed out across a whole wall with no pattern to them, suspect the construction rather than a flood.
3. Surface condensation
A meter pressed against a cold external wall in January will read damp because the surface is damp. That does not tell you anything about the inside of the wall or whether water is coming through it. If the reading is high at the surface, unremarkable when you take a deep-probe or gravimetric sample, and worst in the coldest corners of the room, you have condensation, and the answer involves ventilation and heating rather than a chemical injection. Our dehumidifier running cost calculator covers what the cheap version of that fix costs to run.
How to take readings that mean something
One reading is a number. A pattern of readings is evidence. The difference costs you ten minutes.
- Take a control. Read a wall in the same room that you believe is dry, preferably an internal partition. Everything else is judged against that, which removes most of the argument about what the meter is doing.
- Work up the wall in a profile. Readings at 100mm, 300mm, 600mm, 900mm and 1200mm above the floor, in the same vertical line. Genuine rising damp declines with height and stops around a metre. A leak has a source you can trace. Condensation is worst on the coldest surface, which is often nowhere near the floor.
- Record everything. Date, height, position, room temperature, relative humidity. A phone note is enough. Repeat monthly and the trend will tell you more than any single visit ever could.
- Go outside. Most internal damp has an external cause you can see from the pavement. Blocked gutter, cracked downpipe, failed pointing, render cracks, ground level built up above the damp-proof course, a flower bed against the wall. Look before you spend.
- Photograph the meter in position. Reading and location in one frame. If this ends up in front of a landlord or an ombudsman, that photograph does more work than a written figure.
If the readings point somewhere serious, the next step is a proper diagnosis from someone with no financial interest in the answer. The damp survey cost calculator sets out what that costs and how to tell an independent surveyor from a sales visit. If mould has already taken hold, the mould removal cost calculator covers what putting it right involves. And if you rent, the readings you have just taken are evidence: check where your landlord stands against the statutory deadlines before you accept being told it is condensation caused by your washing.
Damp meter readings: common questions
What is a normal damp meter reading on a wall?
On the WME scale most surveyors use for masonry, below 20% is normal, 20% to 27% is moderate, above 27% is high, and above 35% indicates a serious ongoing water source. For plaster the thresholds are lower: 12% to 15% is dry, 16% to 20% warrants monitoring, and above 20% is confirmed damp. For timber, anything above 20% carries a rot risk.
What does WME mean on a damp meter?
Wood Moisture Equivalent. Resistance meters are calibrated on wood, so when you press one against plaster or brick, the number it shows is what the wood scale would read if the material were wood. It is not the moisture content of the wall. Two walls showing 25% WME can hold completely different amounts of water, which is why WME readings support a diagnosis but cannot make one on their own.
Can a damp meter give a false reading?
Frequently. Hygroscopic salts in old plaster and masonry conduct electricity and pull moisture from the air, so a perfectly dry salted wall can read very high on a pin meter. Foil-backed plasterboard, metal lath, plumbing, cables, wallpaper backing and some paints will all send a pinless meter to the top of its scale on a bone dry wall. The meter measures conductivity, and it is your job to work out what is conducting.
What reading means rising damp?
No reading proves rising damp. Genuine rising damp produces a declining moisture profile with height, roughly the bottom metre of the wall, with a salt band at the top edge, and it needs confirming by drilling samples at different heights and testing them gravimetrically as described in BRE Digest 245. A high surface reading at skirting level is equally consistent with a leak, condensation on a cold wall, or salts. If someone diagnoses rising damp from a surface meter alone, get a second opinion.
What is the difference between a pin and pinless moisture meter?
A pin meter measures electrical resistance between two prongs pushed into the surface, giving a genuine moisture content on timber and a WME figure on anything else. A pinless meter uses radio frequency through a flat pad to read up to about 20mm to 40mm deep without marking the surface, but it reports an arbitrary relative scale rather than a percentage. Pinless is for finding where the wet area is. Pin is for measuring how wet it is.
How do I take a reading properly?
Take several, not one. Work in a grid across the affected wall and a matching grid on a wall in the same room you believe is dry, so you have a control. Record height above floor for each, because the profile up the wall is more informative than any single figure. Note the room temperature and humidity too. One reading is a number, a pattern is evidence.
Should I buy a damp meter?
A cheap pin meter costing £15 to £30 is genuinely useful for tracking whether a wall is drying out over weeks, because you are comparing readings against each other rather than against an absolute threshold. It is not useful for diagnosis, and it will not tell you what is causing the damp. For that you need someone who can interpret the whole picture.