Free engineering calculator

An engineering calculator for every size you have to pick

SizingKit is 97 free engineering calculators on one site — conductor and breaker, duct and pipe, feed and speed, beam and bolt — and each of them prints the code table, standard or definition its answer came out of, right beside the answer. There is no signup, no paid tier and nothing uploaded: the arithmetic is JavaScript running in this tab, against tables compiled 2026-09-05 from NEC 2023, the plumbing codes, the ASHRAE Handbook and the ASME, ASTM and ISO standards each trade works to. Start with the console below — 23 quantities and 124 units — or pick the decision you actually came here to make.

100% free
No signup
97 calculators
124 units in one console
Every figure sourced

Convert a reading

Twenty-three quantities, 124 units. Pick the quantity, type the figure in front of you, and every other unit of it comes back at once.

Quantity

Value

A unit you type beats the one selected: 3.5 kW in a field set to hp reads as kilowatts.

—

Power in every unit this site reports it in
W	—
kW	—
hp	—
BTU/h	—
MBH	—
tons (refrig.)	—
MW	—

Type a figure above and the set fills in.

Six trades name one quantity six ways, and two of the names mislead. MBH is a thousand BTU/h — the M is the Roman numeral, so an 80 MBH furnace is 80,000 BTU/h. A ton here is refrigeration capacity, 12,000 BTU/h by definition, and has nothing to do with the ton in Mass or the tons-force in Force.

What are you deciding?

Twelve of the decisions this site is built to make. Each one lands on the page that makes it, with the table it read printed beside the answer.

Nine sections, and what each one decides

The catalog below is the whole site. These are the nine groups it is split into and the kind of decision each one makes, so you can jump straight to the right dozen pages rather than reading ninety-seven names.

Electrical13 pages: The conductor, the raceway it runs in and the device at each end of it — sized against NEC (NFPA 70) 2023 ampacity, fill and overcurrent tables, with the small-conductor cap and the voltage-drop budget weighed against each other rather than reported one at a time.
Power & current7 pages: Watts, volt-amperes, amps and amp-hours converted in every direction, with the power factor and the phase configuration taken as inputs. An assumed unity power factor is what makes most converters wrong the moment a motor is involved.
Electronics10 pages: Bench and panel arithmetic: Ohm's law, dividers, resistor codes, LED series resistors and RC time constants, then the battery, UPS and runtime figures that fall out of them.
HVAC & refrigeration16 pages: Loads, airflow, duct and psychrometrics on the design side; superheat, subcooling and line-set charge on the gauge side. The pressure-temperature data is interpolated between anchors every 20 °F and the pages that use it say so and give the worst case.
Pipe & pumps11 pages: True inside diameters rather than nominal names, friction by Darcy-Weisbach with the factor solved and by Hazen-Williams where the method holds, drainage slope under both the IPC and the UPC, and the four separate terms that add up to a pump's total head.
Machining12 pages: Drills, threads, cutting speeds, chip loads, surface finish and ISO fits — the charts that live inside a toolbox lid, generated from the standards that define them rather than transcribed from another website.
Sheet metal & stock10 pages: Gauge to thickness under four different standards that disagree about the same gauge number, bend allowance and deduction from a K-factor you measured, air-bend tonnage, and what a length of any of it weighs.
Mechanical9 pages: Sections, beams, springs, bolts, gears, belts and cylinders: the arithmetic between a drawing and a part that holds, with the section properties and the material modulus as separate, visible inputs.
Energy & cost9 pages: What a load costs to run at the tariff you type in, what a generator or a solar array has to deliver, and how much heat an envelope loses for a heating system to replace.

All 97 calculators

Every page runs in this tab, answers in both unit systems, and prints the table, code article or definition its answer rests on. Each one also carries four to six links onward to the pages a person reaches for next, so a job that starts at a load and ends at a conduit size never needs the back button.

Electrical

13 tools

Power & current

7 tools

Electronics

10 tools

HVAC & refrigeration

16 tools

Pipe & pumps

11 tools

Machining

12 tools

Sheet metal & stock

10 tools

Mechanical

9 tools

Energy & cost

9 tools

How to get a number you can hand to somebody

Three steps, and the third is the one that separates a calculator from a citation.

Convert what is actually in front of you
Pick the quantity in the console, type the figure off the nameplate, the gauge or the catalog, and read every other unit of it at once — kW against horsepower, psi against inches of water column, CFM against liters per second. Two of the twenty-three entries are temperature, and choosing between them matters: a reading and a difference are not the same conversion, and 10 °F of superheat is 5.6 °C of superheat, not −12.2 °C.
Pick the decision, not the section
Under the console are twelve decisions in the words somebody would use out loud — what conductor, what breaker, what duct, what pipe, what feed and speed, what flat blank. Each lands on the one page that makes that decision, and the catalog further down opens all ninety-seven. Nothing here is behind a search box, because a search box assumes you already know what the page is called.
Read what the answer rests on, not just the answer
Every result on this site is printed next to the table, code article or definition it came out of, and next to the assumptions it made — the ambient temperature, the conductor material, the tool material, the water temperature. Where three limits could have decided the size, the page says which one did and what the answer becomes if you relax it. That last sentence is the one you can take to somebody who wants the number justified.

Technical specifications

Calculators	97 pages in 9 sections — HVAC and refrigeration is the largest at 16, Power & current the smallest at 7
Quantity console	23 quantities, 124 units — including inches of water column, MBH, SFM, feet of head, tons of refrigeration and the US liquid gallon
Codes and standards	NEC (NFPA 70) 2023 · IPC 2021 and UPC · ASHRAE Handbook—Fundamentals, 62.1 and 62.2 · ACCA Manual J, D and S · ASME B36.10M and B1.1 · ASTM B88, E140 and A6 · ANSI/ASME B94.11M · ISO 286 · SAE J429
Tables compiled	2026-09-05 — every figure carries its own source line, and a page names the edition rather than saying "current code"
Unit systems	Both, on every page: imperial and metric side by side, never a toggle that hides one of them
Measurement input	Feet-inches-fractions (12' 6 3/8"), decimal feet, inches, yards, meters, centimeters and millimeters — read by one parser, site-wide
Runs on a server	Nothing. Static HTML plus JavaScript in your own tab: no API call, no account, no upload and no quote form
Past the end of a table	Refused rather than extrapolated — the page says where the table stops and what to read instead

Frequently asked questions

Which code editions are these tables from?

NEC (NFPA 70) 2023 for everything electrical, the 2021 International Plumbing Code for drainage and fixture units with the Uniform Plumbing Code carried alongside it where the two disagree, and the ASHRAE Handbook—Fundamentals plus ACCA Manual J, D and S for the HVAC work. Machining and metals come from ANSI/ASME B94.11M, ASME B1.1, ISO 286, ASTM E140 and SAE J429. The tables were compiled 2026-09-05, and each figure carries its own article or table number so a single number can be checked without trusting the site as a whole.

Does any of it work with no signal?

Yes, once a page has finished loading. The calculators are JavaScript doing arithmetic in your tab against tables that shipped inside the page, so there is no request to make from a mechanical room, a crawlspace or a shop with no bars — and nothing to send anywhere even if there were. The part that needs a connection is the first load, so open what you expect to need before you go down there.

Why does my answer differ from my supplier's chart?

Usually because the two of you are reading different tables, and this site names the one it read. A gauge number is the classic case: 16 gauge is four different thicknesses depending on whether the sheet is steel, galvanized, stainless or aluminum, and a supplier quotes the standard for what they sell. After that it is an assumption you can see and change — the ambient temperature behind an ampacity, the conductor material, the pipe roughness — or the voltage-drop K method, which ignores reactance and drifts above roughly 1/0 conductor size, which the page tells you where it uses it.

Can I print the charts and take them with me?

Yes, and they are laid out for paper rather than only for a screen. Printing a chart page drops the header, footer, ads, FAQ and everything else around the table, repeats the table's own header row at the top of each sheet, and stops rows splitting across a page break. That is deliberate rather than incidental: a large share of what this site publishes ends up taped inside a panel door or a toolbox lid, where it has to be legible without a browser.

Is this a substitute for an engineer, or for the inspector?

No, and every page that touches something a permit governs says what a professional does there that the page cannot. The site reproduces published tables and does the arithmetic on them; it never issues a verdict that an installation is safe or that it passes. A service load calculation, a beam, a Manual J and a fault current study all end with somebody's stamp on them, and the job here is to get the number right up to the point where that stamp is required.

What does the console do that the converter on my phone does not?

Three things: temperature differences, inches of water column, and the units only these trades write in. A general converter will turn a 10 °F superheat into −12.2 °C by treating a difference as if it were a reading, which is out by 40 degrees and sends a technician after refrigerant a system does not need. This console keeps readings and differences apart as two separate quantities, and it carries MBH, SFM, in. w.c., feet of head, tons of refrigeration and the US liquid gallon, which is most of what a nameplate, a manometer and a pump curve are actually written in.

About sizing something, and then defending the size

Almost nothing on this site is a single calculation. Sizing a conductor weighs at least three limits against each other at once — the ampacity of the insulation at the ambient temperature it will actually sit in, the small-conductor rule that caps what 14, 12 and 10 AWG may be protected at whatever their ampacity says, and how much voltage the run can afford to lose — and only one of them decides the answer. Every competitor returns the winner and stops. The wire size calculator here names the limit that bound the result, so that when somebody asks why the wire came out a size larger than they expected, the reply is a sentence with a table behind it rather than a shrug. The voltage drop calculator is that second limit on its own, and it prints the awkward fact along with it — the 3% and 5% figures everyone quotes live in an informational note, and an informational note is not an enforceable requirement of the code.

Half of what this site publishes is not a calculation at all but a table, and a table has its own kind of honesty problem. A gauge number means nothing without the standard it was read from, so the wire gauge chart gives the AWG geometry computed from the gauge definition rather than retyped from anywhere — a transcribed table has typos and a generated one cannot. The drill size chart merges the fractional, number, letter and metric series into one sorted list because a shop owns all four and the nearest size is rarely in the series you started in. And the conduit fill calculator applies the 31% limit that exists for exactly two conductors, which most fill calculators quietly skip because it is the one row of Chapter 9 Table 1 that does not follow the pattern. Where a table simply stops — a hardness conversion past the range its standard covers, a horsepower the motor table leaves blank — the page stops with it and says so, because an interpolated ampacity is worse than no answer.

The rest is arithmetic that is true everywhere, and it belongs in code where it can be read rather than in a table where it can be mistyped. The Ohm’s law calculator and the voltage divider calculator show the identity they solved beside the result for that reason, and the BTU calculator labels its own rule-of-thumb figures as exactly that, along with what a real room-by-room load calculation would change about them. That distinction runs through the whole site: a figure that is definitional — a ton of refrigeration is 12,000 BTU/h, an inch is 25.4 mm — is stated as a fact, and a figure that genuinely moves with alloy, coolant, supplier or water temperature arrives as a field already filled in with ours, with what shifts it written next to it and your number taking precedence the moment you type it.

What happens to the figures you type

Every number on this page is worked out by JavaScript running in the tab you are reading it in. Nothing you type — loads, lengths, nameplate ratings, the rates your utility charges you — is uploaded, logged or kept, which is also why the calculators carry on working in a mechanical room with no signal.

The console above is the clearest case. A nameplate rating, a gauge pressure and a fluid’s specific gravity are converted by arithmetic in this tab and are gone on reload — there is no account for them to hang off, no quote form for them to feed, and no supplier on the other end of this site who would find them interesting.