SettingsSettings for this calculationUS
The sloped roof run from eave to ridge to be covered in slate.
Measure the full slope length along the roof surface from the eave edge to the ridge, not the horizontal run.
The portion of each slate exposed to weather in the finished course.
Weather exposure depends on the slate's length and the required headlap for the roof's pitch — check the slate manufacturer's exposure table for your slate size and pitch.
Slate courses needed
32 courses
They open the calculator with your figures already in it
Slate Shingle Course Calculator: 32 courses — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
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How this was calculated
Formula source(s)
- Course count = ceil(roof run length ÷ slate exposure), the same course-layout method used for wood shingles, applied to slate's typical weather exposure
Inputs used
- Roof Run Length (Eave to Ridge)
- 19.5 ft
- Slate Weather Exposure
- 7.5 in
What this calculation does not cover
- Every course is treated as sitting at the one exposure you enter, because the run is divided once by that single figure — a roof set out with a tighter gauge over the first courses at the eaves, or eased across the whole slope to swallow an awkward last course, will not land on this number.
- The division counts exposure steps between the eave and the ridge, so the doubled eaves course, which shares the first step with the slate above it, adds no step here and no extra row to the count, and neither does the ridge closure.
- A part course is rounded up to a whole one, which leaves the whole of the leftover run sitting in the final course under the ridge rather than being shared out along the slope as a slater would normally close the gauge.
- The exposure figure is taken entirely on trust: anything from 1 cm (0.39 in) to 30 cm (12 in) is accepted, and because neither slate length nor roof pitch is asked for, a margin far too open for the slate you have still comes back as a clean whole number of courses.
- Roof width never enters the arithmetic, so the answer stops at courses — how many slates stand in each course, the total slate order, and the running metres of batten those courses call for all depend on the eave-to-rake dimension this page does not collect.
- One eave-to-ridge run is handled at a time, so a slope interrupted by a dormer, a mansard with a pitch break, or two planes of different height each need their own run entered and the course counts kept separate.
Estimated cost — your price
This site holds no price list for this material — local prices vary too much to publish honestly. Enter your supplier's price and the result is costed with it.
Part of a bigger job
This trade is one line of a job takeoff. Run the whole job and every other trade comes back with it, off the same measurements.
also measures11 other trades
Computed in your browser — nothing you enter is uploaded. Presented in US customary units and US trade terminology. Where a formula follows a published standard, that standard and its edition are cited beside it on this page; where none governs, the page says so. Local amendments override model codes — verify against the code in force where you build.
Sources checked 2026-09-05 · in the site-wide review of 2026-09-06 · v1.0.1
Regulatory standards & verification citations1
- Course count = ceil(roof run length ÷ slate exposure), the same course-layout method used for wood shingles, applied to slate's typical weather exposure
Cite this page
Your workspace
Most jobs need more than one number. Add the calculators you need next and they open right here, underneath this one — your figures stay on screen and nothing is lost to a page change.
Tools and safety for this job
To lay shingles and batten and tile or slate the roof. Generic types, no brands, no prices.
Protection this work requires
- Cutting or grinding concrete, masonry, screed, tile or fibre-cement board releases respirable silica: cut wet or extract at the tool, and wear a P2/N95 respirator at minimum — a nuisance dust mask does not filter it.
- Saws, grinders and breakers run above 85 dB, where hearing damage accumulates and does not recover: defenders or plugs for every cut, not just the long ones.
- Breakers and grinders cause permanent nerve damage: limit continuous trigger time, keep hands warm, and stop if fingers tingle or blanch.
- Boards, blocks and bagged material cause most lasting back injuries on small sites: two people or a lifter for full sheets, and never a bag on one shoulder up a ladder.
- Most fatal falls on small jobs are from under three metres: use a tower or a ladder tied at the top, and never work off the top two rungs.
- Knives cause more site injuries than any power tool: cut away from your body, change blades often, and wear cut-resistant gloves to EN 388 level C for repeated cutting.
Lay shingles: Roof work is the commonest cause of serious fall injury on domestic sites. Edge protection or a properly erected tower is the equipment that matters most here, and a roof that is steep, high, brittle or wet is a job for a roofer with the right access, not a longer ladder.
Show the 8 tools this job needsHide tools
Essential
Chalk line
Claw hammer
Extension ladder
Hand saw
Tape measure
Tower scaffold or trestles
Utility knife
Recommended
Angle grinder
Also needed as materials: chalk refill, cutting and diamond discs, replacement blades.
what each roofing tool is for, and the spec that decides which to buy where one does.