{"success":true,"version":"v1","request":{"tool":"get_calculator_schema","calculator_id":"decking"},"result":{"entity_type":"calculator","id":"decking","calculator_id":"decking","canonical_url":"https://tttkmbb.com/construction/decking","name":"Decking Calculator","title":"Decking Calculator – Deck Boards, Joists and Screws from Deck Size, Board Width, Gap and Joist Spacing","category":"construction","category_name":"Construction & Home","tool_name":"estimate_decking_materials","featured_mcp_tool":false,"description":"Estimates the number of deck boards (rows of boards across the width, board lengths along the length, plus waste), the joists at a given spacing and the screws at two per board per joist for a rectangular deck.","use_when":"You need a material list for a rectangular timber or composite deck: boards, joists and fasteners.","do_not_use_when":"You need structural sizing of joists and beams (span tables depend on species, grade and load; see the AWC DCA 6 guide) or stairs to the deck (use stairs).","inputs":[{"name":"unit_system","label":"Unit system","type":"enum","required":false,"default":"metric","values":[{"value":"metric","label":"Metric (m, cm, mm, m²)","aliases":["si","metres","meters"]},{"value":"imperial","label":"Imperial / US customary (ft, in, ft²)","aliases":["us","feet","inches"]}],"description":"Unit system of the length inputs (metric: m / cm / mm; imperial: ft / in). Outputs are reported in both systems.","example":"metric"},{"name":"deck_length","label":"Deck length (board direction)","type":"number","unit":"m or ft","required":true,"max":1000,"exclusive_min":0,"description":"Deck dimension parallel to the boards (m or ft). Joists run across this direction.","example":4},{"name":"deck_width","label":"Deck width","type":"number","unit":"m or ft","required":true,"max":1000,"exclusive_min":0,"description":"Deck dimension across the boards (m or ft); equals the joist length.","example":3},{"name":"board_width","label":"Board width","type":"number","unit":"mm or in","required":false,"max":1000,"exclusive_min":0,"description":"Actual face width of one board. Default 140 mm (metric) or 5.5 in (imperial, a nominal 2 × 6 or 5/4 × 6).","example":140},{"name":"board_gap","label":"Gap between boards","type":"number","unit":"mm or in","required":false,"min":0,"max":100,"description":"Drainage gap between boards. Default 5 mm (metric) or 3/16 in = 0.1875 in (imperial).","example":5},{"name":"board_length","label":"Board length","type":"number","unit":"m or ft","required":false,"max":100,"exclusive_min":0,"description":"Length of the boards you will buy. Default 3.6 m (metric) or 12 ft (imperial).","example":3.6},{"name":"joist_spacing","label":"Joist spacing","type":"number","unit":"mm or in","required":false,"max":2000,"exclusive_min":0,"description":"Centre-to-centre joist spacing. Default 400 mm (metric) or 16 in (imperial); composite boards laid diagonally usually need 300 mm / 12 in.","example":400},{"name":"waste_percent","label":"Waste allowance","type":"number","unit":"%","required":false,"default":5,"min":0,"max":50,"description":"Extra material for cuts, breakage and offcuts, applied as a multiplier (1 + waste_percent/100). 5 % for straight decking; 10–15 % for diagonal or picture-frame patterns.","example":5}],"outputs":[{"name":"area_m2","label":"Deck area","type":"number","unit":"m²","decimals":2,"description":"deck_length × deck_width."},{"name":"area_ft2","label":"Deck area","type":"number","unit":"ft²","decimals":2,"description":"Deck area in square feet."},{"name":"board_rows","label":"Rows of boards","type":"integer","decimals":4,"description":"ceil(deck_width / (board_width + board_gap))."},{"name":"linear_length_m","label":"Total board length","type":"number","unit":"m","decimals":2,"description":"board_rows × deck_length, before waste."},{"name":"linear_length_ft","label":"Total board length","type":"number","unit":"ft","decimals":2,"description":"Same in feet."},{"name":"boards_needed","label":"Boards to buy","type":"integer","decimals":4,"description":"ceil(linear_length × (1 + waste_percent/100) / board_length)."},{"name":"joists","label":"Joists","type":"integer","decimals":4,"description":"floor(deck_length / joist_spacing) + 1, each as long as deck_width (rim joists included in the count, beams/posts not)."},{"name":"screws","label":"Screws (approx.)","type":"integer","decimals":4,"description":"board_rows × joists × 2."}],"input_schema":{"type":"object","properties":{"unit_system":{"description":"Unit system of the length inputs (metric: m / cm / mm; imperial: ft / in). Outputs are reported in both systems.","type":"string","enum":["metric","imperial"],"default":"metric","examples":["metric"]},"deck_length":{"description":"Deck dimension parallel to the boards (m or ft). Joists run across this direction. Unit: m or ft.","type":"number","maximum":1000,"exclusiveMinimum":0,"examples":[4],"x-unit":"m or ft"},"deck_width":{"description":"Deck dimension across the boards (m or ft); equals the joist length. Unit: m or ft.","type":"number","maximum":1000,"exclusiveMinimum":0,"examples":[3],"x-unit":"m or ft"},"board_width":{"description":"Actual face width of one board. Default 140 mm (metric) or 5.5 in (imperial, a nominal 2 × 6 or 5/4 × 6). Unit: mm or in.","type":"number","maximum":1000,"exclusiveMinimum":0,"examples":[140],"x-unit":"mm or in"},"board_gap":{"description":"Drainage gap between boards. Default 5 mm (metric) or 3/16 in = 0.1875 in (imperial). Unit: mm or in.","type":"number","minimum":0,"maximum":100,"examples":[5],"x-unit":"mm or in"},"board_length":{"description":"Length of the boards you will buy. Default 3.6 m (metric) or 12 ft (imperial). Unit: m or ft.","type":"number","maximum":100,"exclusiveMinimum":0,"examples":[3.6],"x-unit":"m or ft"},"joist_spacing":{"description":"Centre-to-centre joist spacing. Default 400 mm (metric) or 16 in (imperial); composite boards laid diagonally usually need 300 mm / 12 in. Unit: mm or in.","type":"number","maximum":2000,"exclusiveMinimum":0,"examples":[400],"x-unit":"mm or in"},"waste_percent":{"description":"Extra material for cuts, breakage and offcuts, applied as a multiplier (1 + waste_percent/100). 5 % for straight decking; 10–15 % for diagonal or picture-frame patterns. Unit: %.","type":"number","minimum":0,"maximum":50,"default":5,"examples":[5],"x-unit":"%"}},"additionalProperties":false,"required":["deck_length","deck_width"]},"output_schema":{"type":"object","properties":{"area_m2":{"description":"deck_length × deck_width. Unit: m².","type":"number","x-unit":"m²"},"area_ft2":{"description":"Deck area in square feet. Unit: ft².","type":"number","x-unit":"ft²"},"board_rows":{"description":"ceil(deck_width / (board_width + board_gap)).","type":"integer"},"linear_length_m":{"description":"board_rows × deck_length, before waste. Unit: m.","type":"number","x-unit":"m"},"linear_length_ft":{"description":"Same in feet. Unit: ft.","type":"number","x-unit":"ft"},"boards_needed":{"description":"ceil(linear_length × (1 + waste_percent/100) / board_length).","type":"integer"},"joists":{"description":"floor(deck_length / joist_spacing) + 1, each as long as deck_width (rim joists included in the count, beams/posts not).","type":"integer"},"screws":{"description":"board_rows × joists × 2.","type":"integer"}}},"formula":"rows = ceil(deck_width / (board_width + board_gap)); linear = rows × deck_length; boards = ceil(linear × (1 + waste/100) / board_length); joists = floor(deck_length / joist_spacing) + 1; screws = rows × joists × 2.","method":"Assumes boards run parallel to deck_length and joists perpendicular to them at the given spacing, with a joist at each end. Ledger, beams, posts, blocking and stair framing are not included.","sources":[{"name":"American Wood Council – DCA 6 Prescriptive Residential Wood Deck Construction Guide","url":"https://awc.org/wp-content/uploads/2022/02/AWC-DCA62012-DeckGuide-1405.pdf","type":"standard","retrieved_at":"2026-09-23"},{"name":"Trex – How to space deck boards (3/16 in side gap)","url":"https://www.trex.com/deck-ideas/how-to-space-deck-boards/","type":"reference","retrieved_at":"2026-09-23"}],"freshness":{"type":"static","max_age_seconds":null,"note":"Deterministic formula with fixed constants; results never go stale. Inputs supplied by the caller determine the output."},"examples":[{"name":"4 m × 3 m deck, 140 mm boards, 5 mm gap, 3.6 m boards, 400 mm joists, 5 % waste","inputs":{"unit_system":"metric","deck_length":4,"deck_width":3,"board_width":140,"board_gap":5,"board_length":3.6,"joist_spacing":400,"waste_percent":5},"expected":{"area_m2":12,"area_ft2":129.17,"board_rows":21,"linear_length_m":84,"boards_needed":25,"joists":11,"screws":462},"url":"https://tttkmbb.com/api/v1/calculate/decking?unit_system=metric&deck_length=4&deck_width=3&board_width=140&board_gap=5&board_length=3.6&joist_spacing=400&waste_percent=5"},{"name":"16 ft × 12 ft deck, 5.5 in boards, 3/16 in gap, 16 ft boards, 16 in joists, 5 % waste","inputs":{"unit_system":"imperial","deck_length":16,"deck_width":12,"board_width":5.5,"board_gap":0.1875,"board_length":16,"joist_spacing":16,"waste_percent":5},"expected":{"area_ft2":192,"area_m2":17.84,"board_rows":26,"linear_length_ft":416,"boards_needed":28,"joists":13,"screws":676},"url":"https://tttkmbb.com/api/v1/calculate/decking?unit_system=imperial&deck_length=16&deck_width=12&board_width=5.5&board_gap=0.1875&board_length=16&joist_spacing=16&waste_percent=5"}],"faq":[{"q":"Which way should the boards run?","a":"Boards are usually laid perpendicular to the joists and parallel to the longest deck side to minimise cuts; enter that side as deck_length and buy boards close to it or to a multiple of it."},{"q":"Why two screws per joist?","a":"Face-fixing with two screws (or one hidden clip) at every joist crossing is the standard pattern in manufacturer guides; hidden fastener systems use about one clip per board per joist instead."}],"tags":["decking calculator","deck boards","how many deck boards","joists","deck screws","composite decking"],"related":[{"calculator_id":"fence","reason":"Posts, rails and pickets for the fence around the deck."},{"calculator_id":"stairs","reason":"Steps from the deck to the ground."},{"calculator_id":"board-feet","reason":"Convert lumber dimensions to board feet for pricing."}],"links":{"html":"https://tttkmbb.com/construction/decking","markdown":"https://tttkmbb.com/construction/decking.md","json":"https://tttkmbb.com/construction/decking.json","api":"https://tttkmbb.com/api/v1/calculate/decking","schema":"https://tttkmbb.com/api/v1/calculators/decking","openapi":"https://tttkmbb.com/openapi.json","mcp":"https://tttkmbb.com/mcp"},"version":"v1","updated_at":"2026-09-23"},"timestamp":"2026-09-23T23:23:57Z","next_actions":[{"tool":"run_calculator","calculator_id":"decking","reason":"Run Decking Calculator with the inputs above."}],"links":{"markdown":"https://tttkmbb.com/construction/decking.md"}}