Understanding your result
The headline is the batten length. The stats give the rows per plane, the pieces and the fasteners. The breakdown shows the slope length, the rows at your gauge, the footage, the pieces and the fasteners, and the counter-battens if you ticked them.
The number to remember is the rows, because the gauge sets it and a small change in gauge changes it a lot: a 13-inch gauge on an 18-foot slope gives 17 rows, a 7½-inch gauge 29. The tile calculator and the slate calculator give the exposure that becomes the gauge.
How we calculate this
The plus one is the batten at the eave, under the first course; the rest follow at the gauge to the ridge. The slope comes from the same pitch factor as the rafter length calculator, and the pitch calculator gives it from a pitch in degrees. On site the top and bottom battens are set first and the gauge adjusted slightly so the courses finish evenly at the ridge, which can change the count by one row.
The assumptions behind the numbers
| Assumption | Default | Where it comes from |
|---|---|---|
| Gauge | 13 in | Typical concrete tile exposure; the tile maker’s data sheet gives yours |
| Batten length | 8 ft | Common treated 1×2 and 1×3 stock |
| Rafter spacing | 24 in | Common rafter or truss spacing |
| Fasteners | 1 per crossing | Tile makers’ and code fastening schedules (minimum) |
| Waste | 5% | Estimating practice |
Assumptions last reviewed October 7, 2026.
The calculator does not size the battens for load, does not count the eave riser or tilting fillet some tile systems need, and assumes rectangular planes. The guide to tile and slate weight covers the structure the battens sit on.
Two worked examples
A tile roof at a 13-inch gauge
Two planes with 40-foot eaves, 16-foot run at 6/12, 13-inch gauge, 8-foot battens, rafters at 24 inches.
- Slope: 16 × 1.118 = 17 ft 11 in
- Rows: floor(214.7 ÷ 13) + 1 = 17
- Length: 17 × 40 × 2 × 1.05 = 1,428 ft, 179 pieces
- Fasteners: 17 × 21 × 2 = 714
About 71 feet of batten per square of roof at this gauge.
A slate roof with counter-battens
One plane, 40-foot eave, 15-foot slope, 7½-inch gauge, counter-battens over rafters at 24 inches.
- Rows: 180 ÷ 7.5 + 1 = 25
- Length: 25 × 40 × 1.05 = 1,050 ft, 132 pieces; fasteners 525
- Counter-battens: 21 runs × 15 ft × 1.05 = 331 ft, 42 pieces
Slate’s short gauge nearly doubles the batten per square compared with tile.
Where to find your inputs
Eave length and planes. From the plan; enter identical planes together.
Run and pitch, or slope. From the plan and the pitch, or measured along a rafter.
Gauge. From the tile or slate maker for your pitch.
Common mistakes
- Forgetting the eave batten. The first row is at the eave. Add one.
- One gauge for every tile. The maker sets it for the product and the pitch.
- Joints between rafters. Batten joints must land on a support.
- No counter-battens in a wet climate. Water trapped behind battens rots them.
- Untreated battens. Use treated timber rated for the purpose.
- Not setting out first. Mark top and bottom, then divide; courses should finish evenly at the ridge.
Questions people ask
- How many battens do I need for a tile roof?
- Count rows up each slope: slope length ÷ gauge + 1. A 17 ft 11 in slope at a 13-inch gauge has 17 rows; on two 40-foot planes that is 17 × 40 × 2 = 1,360 feet, 1,428 with 5 percent waste, or 179 battens 8 feet long.
- What is tile gauge?
- The distance between batten centres, which is the tile's exposure: its length minus the headlap the maker requires. Concrete tiles are typically hung at 13 to 14 inches; slate at half of (length − headlap), 7 to 10 inches for common sizes.
- What size are roof battens?
- Usually 1×2 or 1×3 treated softwood in North America (19 × 38 mm or 25 × 50 mm in metric markets), sized for the rafter spacing and the tile weight by the maker or local code. Battens over rafters at 24 inches need to be stiffer than over rafters at 16.
- What are counter-battens for?
- Vertical battens nailed over the rafters (or on the underlay over solid sheathing) that lift the tile battens so water and air can run down the roof beneath them. They are standard in wet and cold climates and on tile over solid decks.
- How are battens fastened?
- One corrosion-resistant nail or screw at every rafter or counter-batten crossing, with batten joints staggered and made over a support. A 40-foot batten over rafters at 24 inches has 21 crossings.
- Do metal roofs use battens?
- Often, as purlins at 24 inches when a metal roof goes over old shingles or on an agricultural frame. The same row arithmetic applies with the purlin spacing as the gauge; the metal screws calculator uses that spacing for the screw rows.