The Fluid Calculator set covers the hydraulics and fluid-dynamics problems engineers and technicians encounter most. Characterize oil performance with the Viscosity Index Calculator, analyze pipe-wall pressure with the Young-Laplace Pressure Calculator, size treatment basins with the Detention Time and Hydraulic Retention Time calculators, and model friction losses in flow systems with the Friction Calculator.
Browse the Popular list to find the most-used tools quickly, or explore the Trending tab for recent picks. Everything here is free, needs no account, and runs on any device.
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Air Flow Rate Calculator From Pressure and DiameterCalculate air flow rate from pressure difference and pipe diameter. Get volumetric flow in m³/s, m³/h and CFM plus velocity using Bernoulli equation.
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Gas Line CalculatorEnter total BTU, pipe length (feet), and pressure (inches water column) to get the recommended gas pipe size and estimated flow rate.
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Round Pool Volume CalculatorCalculate the water volume of a round (circular) swimming pool in US gallons and cubic feet from its diameter and average depth.
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Viscosity Index CalculatorCalculate Viscosity Index easily with kinematic viscosity values at 40°C and 100°C. Determine oil performance and viscosity-temperature relationship for efficient lubricant analysis and selection.
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Mixing Two Fluids Final Temperature CalculatorCalculate the final equilibrium temperature when two fluids are mixed, using mass, specific heat, and starting temperatures. Free physics tool.
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Water Viscosity CalculatorCalculate the dynamic viscosity of water at any temperature using the Vogel relation. Get results in Pa·s, mPa·s and centipoise (cP) instantly.
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Kinematic Viscosity CalculatorCalculate kinematic viscosity (ν) from dynamic viscosity (μ) and density (ρ) using ν = μ/ρ. Get results in m²/s, Stokes, and centistokes.
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Dog Raisin Toxicity CalculatorEstimate your dog's grape or raisin toxicity risk from amount eaten and body weight. Uses conservative toxic-dose thresholds. Not a substitute for a vet.
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Gallon CalculatorConvert a rectangular tank's dimensions (length, width, height in inches) into US gallons. Free volume calculator with cubic inches and liters output.
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GPM Flow Rate Calculator (Pipe)Calculate pipe flow rate in GPM from flow velocity (ft/s) and inside diameter (inches). Free gallons-per-minute calculator using velocity × area × 448.831.
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Water Flow from Pipe Pressure & Diameter CalculatorEstimate water flow rate from pipe pressure and inner diameter using Q = A·√(2P/ρ). Get results in L/min, m³/s, m³/h plus flow velocity.
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Water Flow Rate Through a Hose CalculatorEstimate water flow rate through a hose from inner diameter, supply pressure and discharge coefficient. Get liters/min, GPM and exit velocity instantly.
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Dynamic Viscosity of Water CalculatorCalculate the minimum pipe diameter from volume flow rate and target flow velocity using D = √(4Q/πv). Get diameter in mm and m plus pipe area.
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Speed of Sound in Water CalculatorCalculate the speed of sound in air using a = √(γRT). Enter temperature in °C to get the sonic speed in m/s, km/h, and mph instantly.
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Gallons per Minute from Meter or Bucket Test CalculatorCalculate gallons per minute (GPM) flow rate from a bucket fill test. Enter container volume and fill time in seconds to get GPM and GPH.
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Darcy-Weisbach Head Loss CalculatorCalculate pipe friction head loss with the Darcy-Weisbach equation. Enter friction factor, length, diameter, velocity and gravity to get head loss in meters.
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Hydraulic Gradient CalculatorCalculate the hydraulic gradient (i = dh / L) from head loss and flow path length. Free dimensionless gradient and percent slope calculator for groundwater flow.
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Orifice Flow CalculatorCalculate volumetric flow through an orifice using Q = Cd·A·√(2gh). Enter discharge coefficient, area, head and gravity to get flow rate in m³/s.
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Reynolds Number CalculatorCalculate the Reynolds number from fluid density, velocity, characteristic length and viscosity to determine laminar, transitional or turbulent flow.
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Manning's Pipe Flow CalculatorCompute flow rate (discharge), velocity, area and hydraulic radius in a circular pipe using the Manning equation for full or partially full pipes.
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Specific Gravity to Density CalculatorConvert specific gravity (SG) to density. Multiply SG by the reference water density (1000 kg/m³) to get density in kg/m³, g/cm³ and g/L instantly.
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Hydropower Output CalculatorCalculate hydroelectric power output from water flow rate, head, and efficiency using P = ρgQHη. Results in watts and kilowatts.
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Density Altitude CalculatorCalculate density altitude from field elevation, altimeter setting, and OAT using DA = PA + 120 x (OAT - ISA). Quick pilot performance estimate.
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Water Pressure Loss from Elevation CalculatorCalculate water pressure loss from elevation change using 0.433 psi per foot. Enter elevation in feet and specific gravity to get psi, head, and bar.
Frequently asked questions
What fluid and hydraulics problems can I solve here?
The collection covers flow analysis, piping design, and fluid properties: calculate how long water stays in a treatment tank with the Detention Time Calculator, find capillary or bubble pressure with the Young-Laplace Pressure Calculator, compare lubricant performance across temperatures with the Viscosity Index Calculator, and size a gas line with the Gas Line Calculator.
Are the fluid calculators free?
Yes — every tool on this page is free to use, with no login or download required. They load instantly on any phone, tablet, or desktop browser.
How accurate are the results?
The tools apply established fluid mechanics and hydraulics equations including the Young-Laplace equation, Darcy-Weisbach friction factors, and standard viscosity index formulas. Results are suitable for preliminary analysis and academic work. For any safety-critical or regulatory application — pipeline design, water treatment compliance, pressure vessel specification — verify calculations against the governing engineering code and have a qualified engineer review the work.
Do you store my inputs?
No. Every calculation runs entirely in your browser. Flow rates, pressures, viscosities, and dimensions you enter are never sent to our servers or saved in any way.
Which fluid calculators do users reach for most?
The Popular list ranks tools by real visitor traffic, so the most-used calculators appear at the top. You can also browse Trending for fast-rising tools, Recently Added for the newest entries, or Last Updated for recently revised calculators.
