Roll of electric underfloor heating mat showing its cable and carrier mesh

Electric heating mat sizing

What Size Underfloor Heating Mat Do I Need?

Choose the mat from the free heated area—not the total room area—and prove the full cable route fits before ordering.

Select the largest available mat that fits comfortably without cable being cut, crossed, overlapped or forced beneath permanent objects.

View the Mat Size Table Full System Sizing Guide
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Three Steps to the Right Mat Size

Area is only the first check; the mat shape and cable route must also work.

Calculate the Free Heated Area

Start with gross floor area, then remove permanent exclusions and required clearances. Use the full system-selection guide first if this is not complete.

Draw the Mat Route

Mark long open runs, every turn and narrow passage. Cutting carrier mesh changes direction but does not reduce cable length.

Choose the Nearest Size Below the Limit

Select an available mat that remains inside the free area. Never round up beyond what the dimensioned route can contain.

COVERAGE RULE

What Do 85% and 90% Coverage Mean?

Coverage is the percentage of free floor occupied by the mat. The unheated remainder gives room for edges, turns and irregularities; it is not permission to place cable beneath exclusions.

85% target

Mat area ÷ 0.85

Use this to estimate the free floor area a mat may suit while leaving more room for edges, turns and irregularities.

90% target

Mat area ÷ 0.90

This gives a tighter coverage estimate. It remains a planning aid and never overrides the safe cable route.

Underfloor Heating Mat Size Table

Use this only after calculating the free heated area. Availability, output and the number of individual mats in a kit vary by range and stock, so confirm current product data before ordering.

Mat area Indicative free area at 85% Indicative free area at 90% Typical length if one 0.5m-wide mat
1.0m² 1.18m² 1.11m² 2m
1.5m² 1.76m² 1.67m² 3m
2.0m² 2.35m² 2.22m² 4m
2.5m² 2.94m² 2.78m² 5m
3.0m² 3.53m² 3.33m² 6m
3.5m² 4.12m² 3.89m² 7m
4.0m² 4.71m² 4.44m² 8m
5.0m² 5.88m² 5.56m² 10m
6.0m² 7.06m² 6.67m² 12m
7.0m² 8.24m² 7.78m² 14m
8.0m² 9.41m² 8.89m² 16m
9.0m² 10.59m² 10.00m² 18m
10.0m² 11.76m² 11.11m² 20m
11.0m² 12.94m² 12.22m² 22m
12.0m² 14.12m² 13.33m² 24m

1.0m²

Indicative free area at 85%
1.18m²
Indicative free area at 90%
1.11m²
Typical length if one 0.5m-wide mat
2m

The length column is an illustration for a single half-metre-wide mat. Some larger kits contain more than one mat; always check product contents and dimensions.

Understand the Physical Mat

A calculated area still has to fit through the room as a continuous heating cable.

Understand the roll

How Mat Dimensions Work

Many roll mats in this category are 0.5m wide. For one mat of that width, approximate roll length is area divided by 0.5: a 4m² mat is about 0.5m × 8m and a 6m² mat about 0.5m × 12m.

The mat does not need one straight run. Carrier mesh can normally be cut and turned under the manual while the heating cable remains intact.

Check the real shape

Area Does Not Guarantee a Fit

Narrow passages, multiple exclusions, cold-tail position and the number of individual mats can make a nominal size impractical. Confirm width, length and kit composition from current product data.

WORKED EXAMPLES

Worked Examples

Coverage percentage is useful only when the complete cable route also fits.

Example A

3.4m² Free Heated Area

A 3.0m² mat gives about 88% coverage and leaves 0.4m² for clearances and turns. It is a sensible candidate if the route works. A 3.5m² mat exceeds the free area.

Example B

6.8m² Free Heated Area

A 6.0m² mat gives about 88% coverage. Check whether a 0.5m × 12m roll can turn through the room or whether the current product contains more than one mat.

Example C

Long, Narrow or Broken-Up Area

Even when the calculation suggests a size, the roll may not fit. A smaller mat, two properly designed mats or a loose-cable system may be more practical.

ELECTRICAL CHECK

Check the Complete Electrical Design

The mat must fit physically and work safely with the controls and electrical circuit.

Large or divided area

Can I Use More Than One Mat?

Sometimes, but each mat needs a safe complete route. A qualified electrician must check total load, thermostat rating, circuit capacity, protective devices and switching. Matching combined area alone is not enough.

Separate design decision

Mat Size and Heat Output Are Different

A 4m² mat describes cable area, not watts per square metre. Choose output separately for heat loss, room use, floor build-up and finish. Equal-area mats can have different wattage, limits and electrical loads.

Before Adding a Mat to Your Basket

A five-minute layout check can prevent an oversized mat, impractical route or electrical load mismatch.

Free heated area and dimensioned route checked

Width, length, mat count and cold-tail position confirmed

W/m² output approved for the room and finish

Insulation and complete floor build-up specified

Thermostat, sensor, load and circuit checked

No cable cutting, overlap or permanent exclusions

Heating mat sizing

Frequently Asked Questions

Answers about rounding, coverage, mesh turns and rooms where no standard mat fits.

Should I round my free area up or down?

Choose an available mat that fits at or below the free heated area and works in the route drawing. Do not round up beyond the safe area; the cable cannot be shortened.

Is 90% floor coverage required?

No. It is an estimating target, not a universal installation rule. Heat output, heat loss, exclusions and the actual route matter more than achieving one percentage.

Can I cut the mesh to make turns?

Usually yes if the instructions permit it. Cut only carrier mesh and keep the cable intact, correctly spaced and free from crossings or overlaps.

What if no mat size fits the room?

Use a smaller mat, consider multiple mats with an electrician-approved control design, or choose a loose-cable system that follows an irregular layout more effectively.