{"openapi":"3.1.0","info":{"title":"Gemstone Weight API","version":"1.0.0","description":"Gemstone weight maths as an API, computed locally and deterministically — the carat, gram, point and measured-weight numbers a jeweller, gem dealer, appraiser or lapidary works to. The carat-to-grams endpoint converts a carat weight to grams, milligrams and points: the metric carat is exactly 0.2 g (200 mg) and is split into 100 points, so a 1.5 ct stone is 0.3 g and 150 points and a quarter-carat is a twenty-five pointer — the carat is a mass unit, not a size, so a 1 ct diamond and a 1 ct emerald weigh the same but look different because their densities differ. The grams-to-carat endpoint inverts it (divide grams by 0.2, or multiply by 5), for a weight taken on a gram balance. The round-brilliant-weight endpoint gives the trade estimate used when a stone is set and cannot be put on a scale: carat ≈ diameter² × depth × 0.0061, with the girdle diameter and total depth in millimetres — a 6.5 mm round about 4 mm deep estimates near 1 carat, which is exactly why a 1 ct round brilliant measures roughly 6.5 mm across; the factor can be nudged for a thick girdle or a different cut. Everything is computed locally and deterministically, so it is instant and private. Ideal for jewellery and appraisal tools, gem-dealer and auction apps, and lapidary calculators. Pure local computation — no key, no third-party service, instant. Weight maths only — it does not price the stone or grade the colour and clarity. 3 compute endpoints. For gold karat and fineness use a gold-purity API.","contact":{"name":"PremiumApi","url":"https://www.oanor.com/by/premiumapi"}},"servers":[{"url":"https://api.oanor.com/gemstone-api","description":"oanor gateway"}],"tags":[{"name":"Gemstone"},{"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/carat-to-grams":{"get":{"operationId":"get_v1_carat_to_grams","tags":["Gemstone"],"summary":"Carat to grams, mg and points","description":"","parameters":[{"name":"carat","in":"query","required":true,"description":"Carat weight","schema":{"type":"string"},"example":"1.5"}],"security":[{"oanorKey":[]}],"responses":{"200":{"description":"OK","content":{"application/json":{"example":{"data":{"note":"The metric carat is exactly 0.2 grams (200 mg), and one carat is split into 100 points — so a 1.5 ct stone is 0.3 g and 150 points, and a 0.25 ct stone is a 'twenty-five pointer'. The carat is a mass unit, not a size: a 1 ct diamond and a 1 ct emerald weigh the same but look very different in size because their densities differ.","grams":0.3,"inputs":{"carat":1.5},"points":150,"milligrams":300},"meta":{"timestamp":"2026-06-07T08:17:54.155Z","request_id":"b3f0f3d5-6b3f-4421-b762-d09b58b30fda"},"status":"ok","message":"Carat to grams","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/grams-to-carat":{"get":{"operationId":"get_v1_grams_to_carat","tags":["Gemstone"],"summary":"Grams to carat and points","description":"","parameters":[{"name":"grams","in":"query","required":true,"description":"Weight in grams","schema":{"type":"string"},"example":"0.3"}],"security":[{"oanorKey":[]}],"responses":{"200":{"description":"OK","content":{"application/json":{"example":{"data":{"note":"Grams to carats: divide by 0.2 (or multiply by 5), since a carat is a fifth of a gram. A 0.3 g stone is 1.5 ct. Loose-stone scales read directly in carats, but a weight taken in grams — say on a kitchen or lab balance — converts straight across with this factor.","carat":1.5,"inputs":{"grams":0.3},"points":150,"milligrams":300},"meta":{"timestamp":"2026-06-07T08:17:54.244Z","request_id":"093c3ae7-f092-458c-86f5-f58d72f64dec"},"status":"ok","message":"Grams to carat","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/round-brilliant-weight":{"get":{"operationId":"get_v1_round_brilliant_weight","tags":["Gemstone"],"summary":"Estimated carat of a round brilliant","description":"","parameters":[{"name":"diameter_mm","in":"query","required":true,"description":"Girdle diameter (mm)","schema":{"type":"string"},"example":"6.5"},{"name":"depth_mm","in":"query","required":true,"description":"Total depth (mm)","schema":{"type":"string"},"example":"4.0"},{"name":"factor","in":"query","required":false,"description":"Weight factor (default 0.0061)","schema":{"type":"string"},"example":"0.0061"}],"security":[{"oanorKey":[]}],"responses":{"200":{"description":"OK","content":{"application/json":{"example":{"data":{"note":"When a stone is set and cannot be weighed, the trade estimates a round brilliant's weight from its measurements: carat ≈ diameter² × depth × 0.0061, with the diameter and depth in millimetres. A 6.5 mm round about 4 mm deep estimates near 1 carat — which is why a 1 ct round brilliant is roughly 6.5 mm across. Adjust the factor for a thick girdle or different cut; it is an estimate, not a substitute for a scale.","inputs":{"factor":0.0061,"depth_mm":4,"diameter_mm":6.5},"estimated_carat":1.0309,"estimated_grams":0.20618,"estimated_points":103.09},"meta":{"timestamp":"2026-06-07T08:17:54.332Z","request_id":"f9fe03c4-8a0c-415b-9f1c-6b079e276b45"},"status":"ok","message":"Round brilliant weight","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":"1 carat = 0.2 g = 200 mg = 100 points. Round brilliant estimate: ct ≈ d²·depth·0.0061 (mm). The carat is mass, not size. For gold purity/karat use a gold-purity API.","service":"gemstone-api","endpoints":{"GET /v1/meta":"This document.","GET /v1/carat-to-grams":"Grams, milligrams and points from a carat weight.","GET /v1/grams-to-carat":"Carat and points from a weight in grams.","GET /v1/round-brilliant-weight":"Estimated carat of a round brilliant from diameter and depth."},"description":"Gemstone weight maths: carat to grams/points and back, and the estimated carat of a mounted round-brilliant diamond from its measurements."},"meta":{"timestamp":"2026-06-07T08:17:54.401Z","request_id":"ccc2971a-32af-432c-8906-a58859cd48be"},"status":"ok","message":"Meta","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"}}}}},"x-oanor-pricing":[{"slug":"free","name":"Free","price_cents_month":0,"monthly_call_quota":7300,"rps_limit":2,"hard_limit":true},{"slug":"starter","name":"Starter","price_cents_month":760,"monthly_call_quota":62000,"rps_limit":6,"hard_limit":true},{"slug":"pro","name":"Pro","price_cents_month":2580,"monthly_call_quota":252000,"rps_limit":15,"hard_limit":true},{"slug":"mega","name":"Mega","price_cents_month":7900,"monthly_call_quota":1190000,"rps_limit":40,"hard_limit":true}],"x-oanor-marketplace-url":"https://www.oanor.com/api/gemstone-api"}