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Free Online Water and Environmental Engineering Calculators
Quick, cited calculators for rainwater harvesting, water and wastewater treatment design, laboratory chemistry, groundwater, civil quantities and rooftop solar. Every tool shows its formula, a worked example and the standards it follows.
Water conservation
Rainwater harvesting, leaks, irrigation, demand and groundwater recharge.
- Rainwater harvesting potential calculatorFree rainwater harvesting calculator. Enter roof area and annual rainfall to get litres you can harvest per year, per month and from a heavy rain day.
- Tap drip calculatorHow much water does a dripping tap waste? Count drips per minute and see litres lost per day, month and year, plus the cost.
- Irrigation estimatorEstimate daily and seasonal irrigation water for wheat, rice, sugarcane, vegetables or lawns using reference ET, crop coefficient and irrigation efficiency.
- Drip irrigation calculatorPlan a drip system: number of drippers, total flow, application rate in mm/h, pump size per zone and how long to run it each day.
- First flush volume calculatorSize a first flush diverter: litres to divert from your roof and the pipe length needed for 75, 100 or 150 mm diverter pipes.
- Water demand calculatorCalculate average and peak water demand for a town, township or building using CPHEEO per capita norms, losses, peak factors and population growth.
- Borewell recharge rate calculatorWork out a borewell recharge rate from a field pour test and find how many recharge wells you need to absorb runoff from a heavy storm.
- Infiltration rate calculator (DRIT test)Enter double ring infiltrometer readings to get the infiltration rate for each interval, the steady state rate and the soil permeability class.
Water and wastewater treatment design
Sizing for filters, clarifiers, biological reactors, disinfection and chemical dosing.
- MBBR design calculatorSize a moving bed biofilm reactor (MBBR) from flow and BOD: required biofilm area, media volume, reactor volume, HRT and an air estimate.
- Electrocoagulation calculatorSize an electrocoagulation (EC) cell using Faraday's law: current for a target aluminium or iron dose, electrode area, power, kWh/m³ and electrode use.
- Constructed wetland design calculatorSize a constructed wetland for BOD removal using first order kinetics with temperature correction. Get bed area, HRT, length and width.
- Water softener sizing calculatorSize an ion exchange water softener from daily water use and hardness: resin litres, salt per regeneration, monthly salt and vessel diameter.
- Pressure sand filter calculatorDesign a pressure sand filter (PSF): filter area, vessel diameter, actual filtration rate, backwash flow and water, plus sand and gravel quantities.
- Activated carbon filter calculatorSize an activated carbon filter (ACF) from flow and empty bed contact time: carbon volume, kg of GAC, vessel diameter and bed depth.
- Primary clarifier calculatorDesign a circular primary clarifier: surface area, diameter, overflow rate at average and peak flow, detention time, weir loading and BOD and TSS removal.
- Grit chamber calculatorDesign a horizontal flow grit channel: cross section, width, length with turbulence allowance and detention time from peak flow and settling velocity.
- Water chiller calculatorCalculate chiller capacity in TR, kW, kcal/h and BTU/h from water flow and temperature drop, with safety margin and power estimate.
- RO rejection rate calculatorCalculate reverse osmosis salt rejection, salt passage, recovery, reject flow, reject TDS and concentration factor from feed and permeate data.
- Ozone demand calculatorSize an ozone generator from flow and dose: g/h of ozone, feed gas flow for oxygen or air, contact tank volume, CT and approximate power.
- Chlorine dosage calculatorCalculate chlorine dose for water: kg per day of chlorine, litres of sodium hypochlorite or kg of bleaching powder, dosing pump rate and CT value.
- Lime dosage calculatorCalculate quicklime (CaO) and hydrated lime (Ca(OH)₂) dose for lime softening or for neutralising acidic effluent, in mg/L and kg per day.
Environmental lab
Everyday laboratory chemistry for water testing.
- Normality calculatorFree normality calculator for lab solutions: grams needed for a target normality, normality from mass, N1V1 = N2V2 dilution and dilution of concentrated acids.
- Water hardness calculatorCalculate total hardness as CaCO₃ from calcium and magnesium or from an EDTA titration, convert to ppm, gpg, °dH and mmol/L, and compare with IS 10500.
Soil and groundwater
Hydrogeology, sampling and soil classification.
- Hydraulic gradient calculatorCalculate groundwater hydraulic gradient between two wells, then Darcy flux, seepage velocity and travel time using hydraulic conductivity and porosity.
- Well purge volume calculatorCalculate one well volume and the purge volume for groundwater sampling from casing diameter, well depth and depth to water, with optional filter pack.
- Soil texture calculatorFind the USDA soil textural class from sand, silt and clay percentages, see it on the texture triangle, and get typical permeability.
- Categorisation of groundwater assessment unitsCalculate stage of groundwater extraction and the CGWB GEC-2015 category (safe, semi-critical, critical, over-exploited) for a block, mandal or taluk.
Engineering calculations
Civil quantities and pipe hydraulics.
- RCC tank material estimationEstimate concrete, cement bags, sand, aggregate, steel and shuttering for a rectangular RCC water tank or sump from its size and wall thickness.
- Brick calculatorCalculate the number of bricks, mortar, cement bags and sand for a brick wall, with half or full brick thickness, openings and wastage.
- Friction head loss calculatorCalculate friction head loss in a water pipe from flow, diameter, length and material. Darcy-Weisbach with Swamee-Jain, Hazen-Williams check, minor losses and pump head.
Renewables
Rooftop solar sizing, savings and payback.
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About these tools
Are these engineering calculators free?
Yes. All 31 tools are free, need no sign up and run in your browser. Nothing you type is sent to a server.
What standards are the calculators based on?
Each tool cites its sources: CPHEEO manuals, BIS standards such as IS 10500 and IS 456, CGWB and CGWA guidance, FAO-56, Metcalf and Eddy, US EPA manuals and peer reviewed papers.
Can I use the results for a final design?
They are planning grade estimates for sizing, budgeting and learning. Final designs should be checked by a qualified engineer against site data and current codes.
Can Rispri Labs design or test for my project?
Yes. Rispri Labs designs and builds water, wastewater, ZLD and waste to energy plants, and runs a NABL accredited environmental laboratory in Agra.
Need more than a calculator?
Our engineers design and build treatment plants, and our NABL accredited laboratory tests water, soil, air and waste.