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How it works
From question to a checked result in three steps.
Find the right tool
Type part of a name into the search box, or open a discipline card. Each calculator card shows its category and a short description, so you can tell which tool fits your question before you open it.
Enter your own values
Fill every field with your project data. The fields start empty on purpose, so a value from an earlier job never slips into a new calculation without you noticing.
Read, verify and save
The result appears instantly with the formula and a worked example below it. Compare it with a hand calculation if you like, then download the result as a PDF for your calculation file.
Why engineers use MEP Analysis
Simple, transparent tools. No black boxes.
Formula on every page
You see the equation behind each answer, with the terms explained, so you can defend the number in a design review.
PDF for your records
One click gives you a PDF of the inputs and the result, ready to attach to a calculation sheet or send to a colleague.
Site and office ready
The layout adapts from a phone screen to a desktop monitor, so the same tool works in the site cabin and at your desk.
No account, no cost
There is no signup, login or paywall between you and the calculator. Open a tool and start.
How the calculators fit into one design workflow
MEP calculations are rarely done in isolation. The result of one tool usually becomes the input of the next. This is the order many site and design engineers follow when they check a building service design.
- Estimate the loads. List the lighting, power and equipment loads and work out the cooling load of each space. Separate the connected load (everything installed) from the demand load (what is realistically running together).
- Convert power into current. Use the kW, kVA and amps relationship, together with the power factor and the supply voltage, to find the current each circuit or feeder has to carry.
- Size the cables and check the voltage drop. Pick a conductor that carries the current safely, then confirm that the voltage drop over the actual route length stays within the limit you are designing to.
- Size the water side. Start from the daily water demand, decide the tank and treatment plant capacity, size the pipes for flow and velocity, then calculate pump head and pump power for the chosen route.
- Check fire protection separately. Fire water storage, fire pump flow and pressure loss follow their own rules and reserves, so they are sized on their own and not mixed with the domestic water figures.
- Close the loop. Pump motors, AC compressors and fire pumps all draw electrical power. Add them back to the electrical load list, and repeat the cable and load checks if the total has changed.
Worked examples you can verify by hand
Each calculator on this site shows its own formula, but these four short examples show the kind of arithmetic behind the tools. The numbers are illustrative, so replace them with your project values.
Three-phase load: amps to kW and kVA
A balanced 415 V three-phase load draws 20 A at a power factor of 0.85.
kW = √3 × V × I × PF ÷ 1000
kW = 1.732 × 415 × 20 × 0.85 ÷ 1000
≈ 12.2 kW real power, and 14.4 kVA apparent power
Air conditioner: BTU/h to tons of refrigeration
A room needs 18,000 BTU/h of cooling. One ton of refrigeration (TR) equals 12,000 BTU/h, or about 3.517 kW of cooling.
TR = 18,000 ÷ 12,000
1.5 TR, which is about 5.3 kW of cooling capacity (not electrical input)
Pump: head and power
A pump delivers 30 m³/h against a total dynamic head of 40 m, and its efficiency is 60%.
Hydraulic kW = 9.81 × Q(m³/s) × H(m)
= 9.81 × (30 ÷ 3600) × 40 = 3.27 kW
Shaft kW = 3.27 ÷ 0.60
≈ 5.45 kW at the pump shaft, so choose the next standard motor with a margin
Daily water demand for a residential block
A building has 200 residents. A figure of 135 litres per person per day is commonly used for residential estimates in India, but confirm it against the code or authority that applies to your project.
200 × 135 L = 27,000 L per day
27 m³ per day of domestic demand, before fire reserve and any other uses
Common mistakes the calculators help you catch
Most calculation errors come from small habits, not from hard formulas. Watch for these.
- Mixing kW and kVA. Equipment is often rated in kVA while the load is quoted in kW. The power factor connects them, so do not treat the two as equal.
- Using a single-phase formula for a three-phase load. The √3 factor is easy to forget and changes the answer by about 73%.
- Ignoring derating of cables. High ambient temperature, grouped cables and installation method all reduce the current a cable can safely carry.
- Checking current but not voltage drop. A cable that is thermally safe can still be too thin for a long run.
- Sizing an AC by floor area alone. Sun exposure, occupancy, equipment heat and ventilation air all change the real cooling load.
- Leaving out static head and friction loss. Pump head is more than the height of the tank. Pipe length, fittings and velocity add to it.
- Forgetting pump motors in the electrical load. Water and fire pumps are some of the largest motors in a building.
- Mixing units. CFM and m³/h, feet and metres, BTU/h and kW are easy to confuse. Write the unit next to every number.
Engineering terms in plain words
Short definitions of the terms you will meet in the calculators.
- kW (real power)
- The power that does useful work, such as turning a motor or producing light or heat.
- kVA (apparent power)
- The total power the supply has to provide. It is equal to kW divided by the power factor.
- Power factor (PF)
- The ratio of kW to kVA. A low value means the system carries more current than the useful work needs.
- Connected load
- The sum of the ratings of all installed equipment on a circuit, panel or building.
- Demand load
- The load expected to run at the same time. It is usually lower than the connected load because not everything runs together.
- Voltage drop
- The voltage lost along a cable because of its resistance. Longer runs and higher current increase it.
- TR and BTU/h
- Units of cooling capacity. One TR equals 12,000 BTU/h.
- CFM
- Cubic feet per minute, a common unit for airflow in ducts and ventilation.
- TDH
- Total dynamic head: the total height-equivalent pressure a pump must overcome, including static height and friction losses.
- STP and WTP
- Sewage treatment plant and water treatment plant, sized from the expected daily flow of a building.
How we keep the calculators reliable
Every calculator is built to be checked, not trusted blindly. Each page shows the formula it uses, a worked example and the standard or method it is based on, so you can repeat the calculation by hand and compare the answer.
The tools are meant for estimation, quick checks, learning and early design stages. They do not replace a code review, a site survey or the judgement of a qualified engineer. Read the full Disclaimer for how the results should be used.
If you think a result or an explanation is wrong, or you want a calculator that is not here yet, please use the contact page. Reports of this kind are the most useful feedback we receive, and they help us review and correct the tools.
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About MEP Analysis
MEP Analysis is a free engineering resource for mechanical, electrical and plumbing professionals, students and site engineers. It brings the everyday sizing and checking calculations of building services into one place, with the working shown instead of hidden.
Each calculator is paired with a short explanation of its formula, a worked example and a list of common mistakes. Where a standard or method applies, such as NEC, IS or ASHRAE, it is named on the calculator card so you know what the result is based on.
Results are meant for estimation, learning and early-stage checks. Always verify a final design against the code that applies to your project and with a qualified engineer. Read the full Disclaimer for details.
Frequently asked questions
Quick answers about the calculators and how to use them.
Are the calculators really free?
Yes. Every calculator is free to use and does not need a signup or login.
Which standards do the calculators follow?
It depends on the calculator. Commonly used standards such as NEC, IS and ASHRAE are referred to, and the standard for each tool is shown on its card and on its page.
Can I use the results for final design or construction?
The results are for estimation and learning. Please verify them against the applicable code and with a licensed or qualified engineer before final design or construction.
What is the difference between connected load and demand load?
Connected load is the total rating of everything installed. Demand load is the part of it that is expected to run at the same time. Cables, panels and supply capacity are normally sized on the demand load, using a suitable demand factor.
Why can my result differ from a manual calculation or from another tool?
Small differences usually come from rounding, a different power factor or efficiency, a different standard, or a different unit conversion. Compare the inputs and the formula shown on the calculator page, and the cause is normally easy to find.
Should I add a safety margin to the result?
Most designs add a margin for future expansion and for uncertainty in the inputs. The size of the margin depends on the type of system and on the code or client requirement, so decide it as part of the design and not inside the calculator.
Can students and beginners use these calculators?
Yes. The formulas, worked examples and the glossary on this page are written so that a beginner can follow the steps and see how the answer is reached.
How does this site handle my data?
Calculations run in your browser. For details about cookies and analytics, read our Privacy Policy.
How can I ask for a new calculator?
Send your request through the contact page. Tell us the calculation, the inputs you have and the output you need, and we will consider it for a future addition.
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