{"success":true,"version":"v1","request":{"tool":"get_calculator_schema","calculator_id":"pipe-flow"},"result":{"entity_type":"calculator","id":"pipe-flow","calculator_id":"pipe-flow","canonical_url":"https://tttkmbb.com/engineering/pipe-flow","name":"Pipe Flow Calculator (Hazen–Williams)","title":"Pipe Flow Calculator – Velocity, Head Loss and Pressure Drop of Water with the Hazen–Williams Equation","category":"engineering","category_name":"Engineering & Automotive","tool_name":"calculate_pipe_flow_hazen_williams","featured_mcp_tool":false,"description":"Computes the flow velocity, friction head loss and pressure drop of water in a full-flowing round pipe from flow rate, internal diameter, length and the Hazen–Williams roughness coefficient C, plus an estimated Reynolds number and a velocity check.","use_when":"You are sizing a water supply, irrigation, fire-protection or pump discharge line and need the friction loss for a given flow, or want to check that the velocity stays in the usual 0.6–2.5 m/s range.","do_not_use_when":"The fluid is not water at ordinary temperature (oil, gas, glycol mixtures: use Darcy–Weisbach with the fluid's viscosity), flow is laminar, or the pipe is partly full (open-channel flow).","inputs":[{"name":"flow_rate","label":"Flow rate","type":"number","required":true,"max":10000000,"exclusive_min":0,"description":"Volumetric flow rate in the unit chosen by flow_unit.","example":10},{"name":"flow_unit","label":"Flow unit","type":"enum","required":false,"default":"l_per_s","values":[{"value":"l_per_s","label":"Litres per second (L/s)","aliases":["l/s","lps"]},{"value":"l_per_min","label":"Litres per minute (L/min)","aliases":["l/min","lpm"]},{"value":"m3_per_s","label":"Cubic metres per second (m³/s)","aliases":["m3/s"]},{"value":"gpm_us","label":"US gallons per minute (gpm)","aliases":["gpm","us_gpm"]}],"description":"Unit of flow_rate (1 US gal = 3.785411784 L).","example":"l_per_s"},{"name":"pipe_diameter_mm","label":"Internal diameter","type":"number","unit":"mm","required":true,"max":10000,"exclusive_min":0,"description":"Internal (bore) diameter of the pipe in millimetres; nominal sizes differ from the bore, e.g. DN100 PVC PN10 has about 96 mm bore (1 in = 25.4 mm).","example":100},{"name":"pipe_length_m","label":"Pipe length","type":"number","unit":"m","required":true,"max":1000000,"exclusive_min":0,"description":"Length of straight pipe in metres; add equivalent lengths for fittings and valves if needed (1 ft = 0.3048 m).","example":100},{"name":"hazen_williams_c","label":"Hazen–Williams C","type":"number","required":false,"default":150,"min":20,"max":160,"description":"Roughness coefficient: PVC/PE 150, copper 140, new steel or ductile iron (cement-lined) 130, new cast iron 130, 20-year-old cast iron 100, badly tuberculated pipe 60–80.","example":150}],"outputs":[{"name":"flow_m3_per_s","label":"Flow","type":"number","unit":"m³/s","decimals":6,"description":"Flow rate converted to cubic metres per second."},{"name":"velocity_m_s","label":"Velocity","type":"number","unit":"m/s","decimals":4,"description":"Mean velocity Q / (π d²/4)."},{"name":"head_loss_m","label":"Head loss","type":"number","unit":"m","decimals":4,"description":"Friction head loss over the whole pipe length, in metres of water column."},{"name":"head_loss_per_100m","label":"Head loss per 100 m","type":"number","unit":"m/100 m","decimals":4,"description":"Friction slope expressed per 100 m of pipe."},{"name":"pressure_drop_kpa","label":"Pressure drop","type":"number","unit":"kPa","decimals":3,"description":"ρ g h_f with ρ = 1000 kg/m³ and g = 9.80665 m/s²."},{"name":"pressure_drop_bar","label":"Pressure drop","type":"number","unit":"bar","decimals":4,"description":"Pressure drop in bar (1 bar = 100 kPa)."},{"name":"pressure_drop_psi","label":"Pressure drop","type":"number","unit":"psi","decimals":3,"description":"Pressure drop in pounds per square inch (1 psi = 6.894757 kPa)."},{"name":"reynolds_number_estimate","label":"Reynolds number (estimate)","type":"number","decimals":0,"description":"Re = v d / ν with ν = 1.0e-6 m²/s (water at 20 °C); Hazen–Williams is only valid for turbulent flow (Re above about 4000)."},{"name":"velocity_check","label":"Velocity check","type":"string","decimals":4,"description":"Comparison with the typical 0.6–2.5 m/s design range for water pipes."}],"input_schema":{"type":"object","properties":{"flow_rate":{"description":"Volumetric flow rate in the unit chosen by flow_unit.","type":"number","maximum":10000000,"exclusiveMinimum":0,"examples":[10]},"flow_unit":{"description":"Unit of flow_rate (1 US gal = 3.785411784 L).","type":"string","enum":["l_per_s","l_per_min","m3_per_s","gpm_us"],"default":"l_per_s","examples":["l_per_s"]},"pipe_diameter_mm":{"description":"Internal (bore) diameter of the pipe in millimetres; nominal sizes differ from the bore, e.g. DN100 PVC PN10 has about 96 mm bore (1 in = 25.4 mm). Unit: mm.","type":"number","maximum":10000,"exclusiveMinimum":0,"examples":[100],"x-unit":"mm"},"pipe_length_m":{"description":"Length of straight pipe in metres; add equivalent lengths for fittings and valves if needed (1 ft = 0.3048 m). Unit: m.","type":"number","maximum":1000000,"exclusiveMinimum":0,"examples":[100],"x-unit":"m"},"hazen_williams_c":{"description":"Roughness coefficient: PVC/PE 150, copper 140, new steel or ductile iron (cement-lined) 130, new cast iron 130, 20-year-old cast iron 100, badly tuberculated pipe 60–80.","type":"number","minimum":20,"maximum":160,"default":150,"examples":[150]}},"additionalProperties":false,"required":["flow_rate","pipe_diameter_mm","pipe_length_m"]},"output_schema":{"type":"object","properties":{"flow_m3_per_s":{"description":"Flow rate converted to cubic metres per second. Unit: m³/s.","type":"number","x-unit":"m³/s"},"velocity_m_s":{"description":"Mean velocity Q / (π d²/4). Unit: m/s.","type":"number","x-unit":"m/s"},"head_loss_m":{"description":"Friction head loss over the whole pipe length, in metres of water column. Unit: m.","type":"number","x-unit":"m"},"head_loss_per_100m":{"description":"Friction slope expressed per 100 m of pipe. Unit: m/100 m.","type":"number","x-unit":"m/100 m"},"pressure_drop_kpa":{"description":"ρ g h_f with ρ = 1000 kg/m³ and g = 9.80665 m/s². Unit: kPa.","type":"number","x-unit":"kPa"},"pressure_drop_bar":{"description":"Pressure drop in bar (1 bar = 100 kPa). Unit: bar.","type":"number","x-unit":"bar"},"pressure_drop_psi":{"description":"Pressure drop in pounds per square inch (1 psi = 6.894757 kPa). Unit: psi.","type":"number","x-unit":"psi"},"reynolds_number_estimate":{"description":"Re = v d / ν with ν = 1.0e-6 m²/s (water at 20 °C); Hazen–Williams is only valid for turbulent flow (Re above about 4000).","type":"number"},"velocity_check":{"description":"Comparison with the typical 0.6–2.5 m/s design range for water pipes.","type":"string"}}},"formula":"Q = flow_m3_per_s, d = pipe_diameter_mm / 1000, L = pipe_length_m, C = hazen_williams_c; velocity_m_s = Q / (π d² / 4); head_loss_m = 10.67 × L × Q^1.852 / (C^1.852 × d^4.87); pressure_drop_kpa = 1000 × 9.80665 × head_loss_m / 1000; reynolds_number_estimate = velocity_m_s × d / 1e-6","method":"Hazen–Williams empirical equation in SI form, calibrated for water at about 5–25 °C in turbulent flow with velocities below roughly 3 m/s; outside these conditions (or for other fluids) Darcy–Weisbach with the Colebrook friction factor is more accurate. Minor losses from fittings are not included.","sources":[{"name":"Wikipedia – Hazen–Williams equation","url":"https://en.wikipedia.org/wiki/Hazen%E2%80%93Williams_equation","type":"reference","retrieved_at":"2026-09-24"},{"name":"Wikipedia – Reynolds number","url":"https://en.wikipedia.org/wiki/Reynolds_number","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":"10 L/s through 100 m of 100 mm PVC (C 150)","inputs":{"flow_rate":10,"flow_unit":"l_per_s","pipe_diameter_mm":100,"pipe_length_m":100,"hazen_williams_c":150},"expected":{"flow_m3_per_s":0.01,"velocity_m_s":1.2732,"head_loss_m":1.459,"head_loss_per_100m":1.459,"pressure_drop_kpa":14.308,"pressure_drop_bar":0.1431,"pressure_drop_psi":2.075,"reynolds_number_estimate":127324,"velocity_check":"Within the typical 0.6–2.5 m/s design range"},"url":"https://tttkmbb.com/api/v1/calculate/pipe-flow?flow_rate=10&flow_unit=l_per_s&pipe_diameter_mm=100&pipe_length_m=100&hazen_williams_c=150"},{"name":"400 US gpm through 300 m of 150 mm steel (C 130)","inputs":{"flow_rate":400,"flow_unit":"gpm_us","pipe_diameter_mm":150,"pipe_length_m":300,"hazen_williams_c":130},"expected":{"flow_m3_per_s":0.025236,"velocity_m_s":1.4281,"head_loss_m":4.3979,"head_loss_per_100m":1.466,"pressure_drop_kpa":43.128,"pressure_drop_psi":6.255},"url":"https://tttkmbb.com/api/v1/calculate/pipe-flow?flow_rate=400&flow_unit=gpm_us&pipe_diameter_mm=150&pipe_length_m=300&hazen_williams_c=130"}],"faq":[{"q":"Which C value should I use?","a":"C describes the pipe's interior smoothness: about 150 for new plastic (PVC, PE), 140 for copper, 130 for new steel or cement-lined ductile iron, and 100 or lower for old, corroded cast iron. Designers often use 120–130 for aged metal mains."},{"q":"Does the result include fittings and valves?","a":"No, only straight-pipe friction. Add the equivalent length of each fitting to pipe_length_m, or compute minor losses separately with K × v² / (2g)."},{"q":"Why is the flow velocity limited to about 0.6–2.5 m/s?","a":"Below 0.6 m/s sediment settles and air pockets persist; above about 2.5 m/s friction loss, noise, erosion and water-hammer pressure rise quickly. Pump suction lines are usually kept below about 1.5 m/s."}],"tags":["hazen williams","pipe flow","head loss","friction loss","pipe pressure drop","water velocity"],"related":[{"calculator_id":"pressure","reason":"Convert the pressure drop between kPa, bar, psi and metres of water."},{"calculator_id":"volume","reason":"Convert between litres, cubic metres and gallons."},{"calculator_id":"horizontal-tank-volume","reason":"Liquid volume in the tank the pipe feeds or drains."}],"links":{"html":"https://tttkmbb.com/engineering/pipe-flow","markdown":"https://tttkmbb.com/engineering/pipe-flow.md","json":"https://tttkmbb.com/engineering/pipe-flow.json","api":"https://tttkmbb.com/api/v1/calculate/pipe-flow","schema":"https://tttkmbb.com/api/v1/calculators/pipe-flow","openapi":"https://tttkmbb.com/openapi.json","mcp":"https://tttkmbb.com/mcp"},"version":"v1","updated_at":"2026-09-24"},"timestamp":"2026-09-24T03:44:30Z","next_actions":[{"tool":"run_calculator","calculator_id":"pipe-flow","reason":"Run Pipe Flow Calculator (Hazen–Williams) with the inputs above."}],"links":{"markdown":"https://tttkmbb.com/engineering/pipe-flow.md"}}