Pump Power (HP)
Compute hydraulic and electric power (HP) of a pump given flow, head and efficiency.
—
Hydraulic pump power in HP
To estimate the shaft power a water pump needs, use P (HP) = (Q · H) / (75 · η), where Q is in L/s, H (the manometric head) is in m and η stands for the pump efficiency, which sits around 0.6–0.8 on centrifugal pumps. That 75 is the factor that turns kgf·m/s into HP for water at 1000 kgf/m³. Take Q = 2 L/s, H = 20 m and η = 0.65: P = (2 × 20) / (75 × 0.65) ≈ 0.82 HP, which means you'd spec a 1 HP commercial motor.
Applications
This comes up when you size booster pumps, deep-well pumps, swimming-pool pumps, rural irrigation systems and reservoir transfer pumps on projects that have to meet NBR 12214 and NBR 5626. Round up to the next standard motor size (1/2, 3/4, 1, 1.5, 2 HP…), and keep in mind that H covers the geometric head together with the friction losses along the piping.
FAQ
Why divide by efficiency? No pump turns 100 % of its shaft power into hydraulic power, and η is there to account for the mechanical and hydraulic losses.
What is the manometric head? It's the geometric head plus the pressure you lose across the pipes, fittings and valves.
1 HP equals how many kW? Roughly 0.7457 kW (and 1 cv ≈ 0.7355 kW).
Related Tools
Power by Admiralty Coefficient
Estimate a ship's propulsive power by the Admiralty formula, P = (∆^(2/3)·V³)/C, from the displacement (∆, t), the speed (V, knots) and the Admiralty coefficient (C), characteristic of similar hulls. It is a classic, fast method to predict the required power in the preliminary design stage, based on similarity with existing ships. The V³ dependence shows the high cost of speed. Enter the displacement, the speed and the coefficient C.
Power Factor Calculator
Compute power factor cos(φ) = P/S and angle from active (W) and apparent (VA) power.
Bearing Power Loss
Calculate the power dissipated by friction in a bearing, P = T × ω, multiplying the friction torque T by the angular velocity ω (rad/s). The result, in watts, is the mechanical energy converted to heat per unit time by friction — a loss that reduces efficiency and heats the lubricant and components. This heat must be dissipated (by convection or oil circulation) to keep a safe operating temperature, since overheating degrades the lubricant and can cause seizure. Estimating the dissipated power is essential to size the cooling and the oil flow. Enter the friction torque and the angular velocity.
Rectifier Average Voltage
Calculate the average (DC) voltage of a full-wave rectifier, V_dc = 2 × V_p ÷ π, from the peak voltage V_p of the sinusoidal input. The result, in volts, is the mean value of the pulsating voltage at the rectifier output before filtering — about 63.7% of the peak. A full-wave rectifier (bridge or center-tap) flips the negative half-cycles, doubling the ripple frequency and raising the average voltage compared with a half-wave rectifier (V_p/π). It is the basis of designing DC power supplies from the AC mains. Capacitor filtering then raises the voltage further (close to the peak). Enter the peak voltage.
Brake Power Dissipated
Calculate the power dissipated by a brake under torque, P = T·(2π·n/60), from the braking torque T (N·m) and the rotation n (rpm). Dissipated power is the rate at which the brake converts mechanical energy to heat — the product of braking torque and angular velocity. It differs from total braking ENERGY: energy is the total heat generated (joules), while power is the INTENSITY of that heat generation (watts), and it determines the brake's steady-state temperature. A brake dissipating much energy but slowly (low power) heats little; one dissipating the same energy fast (high power) heats much more. Dissipated power is critical in brakes working CONTINUOUSLY or repetitively: retention brakes on long descents, industrial equipment brakes (hoists, cranes, conveyors holding load), and dynamometers (which measure engine power precisely by dissipating it in a brake). There, the steady-state dissipated power sets the COOLING capacity needed (ventilation, water cooling) to keep temperature stable. Equating dissipated power to cooling capacity gives the equilibrium temperature. Enter the braking torque and the rotation.
Buck Converter (Step-Down)
Calculate the output voltage of a buck (step-down) DC-DC converter in continuous conduction, V_out = D × V_in, from the duty cycle D (0 to 1) and the input voltage V_in. The result, in volts, is always less than or equal to the input — the buck converter lowers voltage efficiently (without dissipating the excess, unlike a linear regulator), by switching rapidly and filtering with an inductor and capacitor. Varying the duty cycle adjusts the output from 0 to V_in. It is the most common topology in switching power supplies and point-of-load regulators. Enter the duty cycle and the input voltage.
The results provided by this tool are for general informational and educational purposes only and do not constitute professional, financial, medical, legal, tax or accounting advice. Always confirm important decisions with a qualified professional and official sources.