{"openapi":"3.1.0","info":{"title":"Rebar Calculator API","version":"1.0.0","description":"Reinforcement-steel (rebar) maths as an API, computed locally and deterministically. The area endpoint computes the cross-sectional area of a reinforcing bar, a = π/4·d², its mass per metre (a·7850/1e6, steel ρ = 7850 kg/m³), the total area and mass for a number of bars, and — given a required steel area — the number of bars needed and the area provided. The spacing endpoint lays out bars across a section: from the width, the cover, the bar diameter and either a centre-to-centre spacing or a bar count it returns the other, n = floor((width − 2·cover − d)/spacing) + 1, the total steel area and the area per metre of width. The ratio endpoint computes the reinforcement ratio ρ = As/(b·d) of a section from the steel area (or the bars) and the section width and effective depth, as a fraction and a percentage, the single number that governs whether a beam is under- or over-reinforced. Everything is computed locally and deterministically, so it is instant and private. Ideal for structural and site-engineering tools, reinforced-concrete detailing, bar-bending schedules and steel take-off, and civil-engineering education. Pure local computation — no key, no third-party service, instant. Live, nothing stored. 3 endpoints. This is rebar geometry and quantities; for concrete mix proportions use a concrete API.","contact":{"name":"PremiumApi","url":"https://www.oanor.com/by/premiumapi"}},"servers":[{"url":"https://api.oanor.com/rebar-api","description":"oanor gateway"}],"tags":[{"name":"Rebar"},{"name":"Meta"}],"components":{"securitySchemes":{"oanorKey":{"type":"apiKey","in":"header","name":"x-oanor-key","description":"Get your key at https://www.oanor.com/developer/keys"}}},"security":[{"oanorKey":[]}],"paths":{"/v1/area":{"get":{"operationId":"get_v1_area","tags":["Rebar"],"summary":"Bar area, mass & count","description":"","parameters":[{"name":"diameter","in":"query","required":true,"description":"Bar diameter d (mm)","schema":{"type":"string"},"example":"16"},{"name":"count","in":"query","required":false,"description":"Number of bars for the total","schema":{"type":"string"},"example":"5"},{"name":"required_area","in":"query","required":false,"description":"Or a required steel area (mm²) to solve the count","schema":{"type":"string"}}],"security":[{"oanorKey":[]}],"responses":{"200":{"description":"OK","content":{"application/json":{"example":{"data":{"note":"Single bar area = π/4·d². Bar mass per metre = area·7850/1e6 (steel ρ = 7850 kg/m³).","count":5,"inputs":{"diameter":16},"total_area_mm2":1005.3096,"bar_mass_kg_per_m":1.57834,"single_bar_area_mm2":201.0619,"total_mass_kg_per_m":7.89168},"meta":{"timestamp":"2026-06-04T18:38:24.961Z","request_id":"653210d4-620e-40a5-8028-1ef8a9fb4aaa"},"status":"ok","message":"Bar area & count","success":true}}}},"401":{"description":"Missing or invalid x-oanor-key header"},"402":{"description":"Active subscription required"},"429":{"description":"Rate-limit or monthly quota reached"},"502":{"description":"Upstream did not respond"}}}},"/v1/ratio":{"get":{"operationId":"get_v1_ratio","tags":["Rebar"],"summary":"Reinforcement ratio","description":"","parameters":[{"name":"width","in":"query","required":true,"description":"Section width b (mm)","schema":{"type":"string"},"example":"300"},{"name":"effective_depth","in":"query","required":true,"description":"Effective depth d (mm)","schema":{"type":"string"},"example":"450"},{"name":"steel_area","in":"query","required":false,"description":"Steel area As (mm²)","schema":{"type":"string"},"example":"1005"},{"name":"diameter","in":"query","required":false,"description":"Or bar diameter (mm) with count","schema":{"type":"string"}},{"name":"count","in":"query","required":false,"description":"and number of bars","schema":{"type":"string"}}],"security":[{"oanorKey":[]}],"responses":{"200":{"description":"OK","content":{"application/json":{"example":{"data":{"note":"ρ = As/(b·d). Typical RC beams run 0.4–2 %; check against the code minimum (≈0.13 %) and maximum (≈4 %).","inputs":{"width":300,"steel_area_mm2":1005,"effective_depth":450},"gross_area_mm2":135000,"reinforcement_ratio":0.007444,"reinforcement_percent":0.7444},"meta":{"timestamp":"2026-06-04T18:38:25.079Z","request_id":"72de68b0-3c64-4e21-8b69-feaa1959f098"},"status":"ok","message":"Reinforcement ratio","success":true}}}},"401":{"description":"Missing or invalid x-oanor-key header"},"402":{"description":"Active subscription required"},"429":{"description":"Rate-limit or monthly quota reached"},"502":{"description":"Upstream did not respond"}}}},"/v1/spacing":{"get":{"operationId":"get_v1_spacing","tags":["Rebar"],"summary":"Section spacing layout","description":"","parameters":[{"name":"width","in":"query","required":true,"description":"Section width (mm)","schema":{"type":"string"},"example":"1000"},{"name":"diameter","in":"query","required":true,"description":"Bar diameter d (mm)","schema":{"type":"string"},"example":"12"},{"name":"cover","in":"query","required":false,"description":"Cover each side (mm, default 25)","schema":{"type":"string"},"example":"25"},{"name":"spacing","in":"query","required":false,"description":"Centre-to-centre spacing (mm) to get the count","schema":{"type":"string"},"example":"150"},{"name":"count","in":"query","required":false,"description":"Or a bar count to get the spacing","schema":{"type":"string"}}],"security":[{"oanorKey":[]}],"responses":{"200":{"description":"OK","content":{"application/json":{"example":{"data":{"note":"Outer bars sit at cover + ½d from each face; n = floor((width − 2·cover − d)/spacing) + 1.","inputs":{"cover":25,"width":1000,"spacing":150,"diameter":12},"spacing_mm":150,"number_of_bars":7,"total_area_mm2":791.6813,"area_per_metre_mm2_m":791.6813},"meta":{"timestamp":"2026-06-04T18:38:25.181Z","request_id":"1a8a6a1c-462a-409a-8365-df88acba3faa"},"status":"ok","message":"Section spacing","success":true}}}},"401":{"description":"Missing or invalid x-oanor-key header"},"402":{"description":"Active subscription required"},"429":{"description":"Rate-limit or monthly quota reached"},"502":{"description":"Upstream did not respond"}}}},"/v1/meta":{"get":{"operationId":"get_v1_meta","tags":["Meta"],"summary":"Spec","description":"","parameters":[],"security":[{"oanorKey":[]}],"responses":{"200":{"description":"OK","content":{"application/json":{"example":{"data":{"notes":"Diameters, widths and depths in mm, areas in mm², mass in kg/m. 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