{"success":true,"version":"v1","request":{"tool":"get_calculator_schema","calculator_id":"compression-ratio"},"result":{"entity_type":"calculator","id":"compression-ratio","calculator_id":"compression-ratio","canonical_url":"https://tttkmbb.com/engineering/compression-ratio","name":"Compression Ratio Calculator","title":"Static Compression Ratio Calculator – Bore, Stroke, Chamber, Piston, Deck and Head Gasket Volumes","category":"engineering","category_name":"Engineering & Automotive","tool_name":"calculate_compression_ratio","featured_mcp_tool":false,"description":"Computes the static compression ratio of a piston engine from bore, stroke, combustion chamber volume and the optional piston dish/dome, deck clearance and head gasket volumes: CR = (swept + clearance) / clearance.","use_when":"You are building or modifying an engine and need the compression ratio after changing heads, pistons, gaskets or deck height.","do_not_use_when":"You need dynamic (effective) compression ratio, which depends on intake valve closing timing, or plain displacement (use engine-displacement).","inputs":[{"name":"bore_mm","label":"Bore","type":"number","unit":"mm","required":true,"max":1000,"exclusive_min":0,"description":"Cylinder bore in millimetres (inches × 25.4).","example":101.6},{"name":"stroke_mm","label":"Stroke","type":"number","unit":"mm","required":true,"max":1000,"exclusive_min":0,"description":"Stroke in millimetres.","example":88.392},{"name":"chamber_volume_cc","label":"Combustion chamber volume","type":"number","unit":"cc","required":true,"max":5000,"exclusive_min":0,"description":"Volume of the cylinder-head combustion chamber in cc (from the head specification or by cc-ing the head).","example":64},{"name":"piston_volume_cc","label":"Piston dish / dome volume","type":"number","unit":"cc","required":false,"default":0,"min":-500,"max":500,"description":"Positive for a dish or valve reliefs (adds clearance volume), negative for a dome, 0 for flat-top.","example":5},{"name":"deck_clearance_mm","label":"Deck clearance","type":"number","unit":"mm","required":false,"default":0,"min":-5,"max":20,"description":"Distance the piston sits below the block deck at TDC (negative if it protrudes).","example":0.635},{"name":"head_gasket_thickness_mm","label":"Head gasket compressed thickness","type":"number","unit":"mm","required":false,"default":0,"min":0,"max":10,"description":"Compressed gasket thickness; 0 to ignore the gasket volume.","example":1.016},{"name":"head_gasket_bore_mm","label":"Head gasket bore","type":"number","unit":"mm","required":false,"max":1000,"exclusive_min":0,"description":"Gasket opening diameter; defaults to the cylinder bore.","example":104.14}],"outputs":[{"name":"compression_ratio","label":"Compression ratio","type":"number","decimals":3,"description":"(swept + clearance) / clearance."},{"name":"compression_ratio_text","label":"Compression ratio","type":"string","decimals":4,"description":"Formatted as n:1."},{"name":"swept_volume_cc","label":"Swept volume","type":"number","unit":"cc","decimals":2,"description":"π/4 × bore² × stroke for one cylinder."},{"name":"deck_volume_cc","label":"Deck volume","type":"number","unit":"cc","decimals":3,"description":"π/4 × bore² × deck_clearance."},{"name":"gasket_volume_cc","label":"Head gasket volume","type":"number","unit":"cc","decimals":3,"description":"π/4 × gasket_bore² × gasket_thickness."},{"name":"clearance_volume_cc","label":"Clearance volume","type":"number","unit":"cc","decimals":3,"description":"chamber + piston + deck + gasket volumes: the volume above the piston at TDC."}],"input_schema":{"type":"object","properties":{"bore_mm":{"description":"Cylinder bore in millimetres (inches × 25.4). Unit: mm.","type":"number","maximum":1000,"exclusiveMinimum":0,"examples":[101.6],"x-unit":"mm"},"stroke_mm":{"description":"Stroke in millimetres. Unit: mm.","type":"number","maximum":1000,"exclusiveMinimum":0,"examples":[88.392],"x-unit":"mm"},"chamber_volume_cc":{"description":"Volume of the cylinder-head combustion chamber in cc (from the head specification or by cc-ing the head). Unit: cc.","type":"number","maximum":5000,"exclusiveMinimum":0,"examples":[64],"x-unit":"cc"},"piston_volume_cc":{"description":"Positive for a dish or valve reliefs (adds clearance volume), negative for a dome, 0 for flat-top. Unit: cc.","type":"number","minimum":-500,"maximum":500,"default":0,"examples":[5],"x-unit":"cc"},"deck_clearance_mm":{"description":"Distance the piston sits below the block deck at TDC (negative if it protrudes). Unit: mm.","type":"number","minimum":-5,"maximum":20,"default":0,"examples":[0.635],"x-unit":"mm"},"head_gasket_thickness_mm":{"description":"Compressed gasket thickness; 0 to ignore the gasket volume. Unit: mm.","type":"number","minimum":0,"maximum":10,"default":0,"examples":[1.016],"x-unit":"mm"},"head_gasket_bore_mm":{"description":"Gasket opening diameter; defaults to the cylinder bore. Unit: mm.","type":"number","maximum":1000,"exclusiveMinimum":0,"examples":[104.14],"x-unit":"mm"}},"additionalProperties":false,"required":["bore_mm","stroke_mm","chamber_volume_cc"]},"output_schema":{"type":"object","properties":{"compression_ratio":{"description":"(swept + clearance) / clearance.","type":"number"},"compression_ratio_text":{"description":"Formatted as n:1.","type":"string"},"swept_volume_cc":{"description":"π/4 × bore² × stroke for one cylinder. Unit: cc.","type":"number","x-unit":"cc"},"deck_volume_cc":{"description":"π/4 × bore² × deck_clearance. Unit: cc.","type":"number","x-unit":"cc"},"gasket_volume_cc":{"description":"π/4 × gasket_bore² × gasket_thickness. Unit: cc.","type":"number","x-unit":"cc"},"clearance_volume_cc":{"description":"chamber + piston + deck + gasket volumes: the volume above the piston at TDC. Unit: cc.","type":"number","x-unit":"cc"}}},"formula":"swept = π/4 × bore² × stroke; deck_volume = π/4 × bore² × deck_clearance; gasket_volume = π/4 × gasket_bore² × gasket_thickness; clearance = chamber_volume_cc + piston_volume_cc + deck_volume + gasket_volume; compression_ratio = (swept + clearance) / clearance (all volumes in cc)","method":"Static (geometric) ratio for one cylinder. Effective compression is lower because the intake valve closes after bottom dead centre; pump-fuel engines typically run 8:1–11:1 naturally aspirated and higher with direct injection.","sources":[{"name":"Wikipedia – Compression ratio","url":"https://en.wikipedia.org/wiki/Compression_ratio","type":"reference","retrieved_at":"2026-09-24"},{"name":"Wikipedia – Engine displacement","url":"https://en.wikipedia.org/wiki/Engine_displacement","type":"reference","retrieved_at":"2026-09-24"}],"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":"350 SBC: 4.00 × 3.48 in, 64 cc heads, 5 cc reliefs, 0.025 in deck, 0.040 in gasket at 4.100 in","inputs":{"bore_mm":101.6,"stroke_mm":88.392,"chamber_volume_cc":64,"piston_volume_cc":5,"deck_clearance_mm":0.635,"head_gasket_thickness_mm":1.016,"head_gasket_bore_mm":104.14},"expected":{"compression_ratio":9.655,"compression_ratio_text":"9.65:1","swept_volume_cc":716.62,"deck_volume_cc":5.148,"gasket_volume_cc":8.654,"clearance_volume_cc":82.802},"url":"https://tttkmbb.com/api/v1/calculate/compression-ratio?bore_mm=101.6&stroke_mm=88.392&chamber_volume_cc=64&piston_volume_cc=5&deck_clearance_mm=0.635&head_gasket_thickness_mm=1.016&head_gasket_bore_mm=104.14"},{"name":"86 × 86 mm, 45 cc chamber, 1 mm gasket at 87 mm, flat piston, zero deck","inputs":{"bore_mm":86,"stroke_mm":86,"chamber_volume_cc":45,"head_gasket_thickness_mm":1,"head_gasket_bore_mm":87},"expected":{"compression_ratio":10.806,"swept_volume_cc":499.56,"gasket_volume_cc":5.945,"clearance_volume_cc":50.945},"url":"https://tttkmbb.com/api/v1/calculate/compression-ratio?bore_mm=86&stroke_mm=86&chamber_volume_cc=45&head_gasket_thickness_mm=1&head_gasket_bore_mm=87"}],"faq":[{"q":"How do I get the chamber volume?","a":"From the cylinder-head specification, or measure it by filling the chamber with liquid from a burette (cc-ing) with the valves and spark plug installed."},{"q":"Does a thicker head gasket lower compression?","a":"Yes: it adds clearance volume. Each 0.25 mm (0.010 in) of gasket on a 100 mm bore adds about 2 cc, roughly 0.2 points of ratio on a 10:1 engine."}],"tags":["compression ratio","static compression","combustion chamber volume","head gasket volume","engine build"],"related":[{"calculator_id":"engine-displacement","reason":"Total displacement from the same bore and stroke."},{"calculator_id":"cylinder","reason":"Cylinder volume geometry."},{"calculator_id":"ideal-gas-law","reason":"Pressure rise of the compressed charge."}],"links":{"html":"https://tttkmbb.com/engineering/compression-ratio","markdown":"https://tttkmbb.com/engineering/compression-ratio.md","json":"https://tttkmbb.com/engineering/compression-ratio.json","api":"https://tttkmbb.com/api/v1/calculate/compression-ratio","schema":"https://tttkmbb.com/api/v1/calculators/compression-ratio","openapi":"https://tttkmbb.com/openapi.json","mcp":"https://tttkmbb.com/mcp"},"version":"v1","updated_at":"2026-09-24"},"timestamp":"2026-09-24T01:52:08Z","next_actions":[{"tool":"run_calculator","calculator_id":"compression-ratio","reason":"Run Compression Ratio Calculator with the inputs above."}],"links":{"markdown":"https://tttkmbb.com/engineering/compression-ratio.md"}}