How the calculators work
Most of electrical work comes back to a handful of relationships. Ohm's Law ties voltage, current and resistance together as V = I ร R, and power follows as P = V ร I. Voltage drop matters because wire has resistance too, so a long run loses some voltage before it reaches the load โ the calculator uses the conductor's cross-section (in circular mils) and material to estimate it. BTU sizing turns a room's dimensions into the cooling capacity an air conditioner needs. The resistor tool decodes the colour bands printed on a component, bandwidth converts a file size and connection speed into a transfer time, and the IP subnet tool breaks an address and prefix into its network, broadcast and usable host range.
The evolution of energy in the world
Every calculator on this page ultimately deals with the same thing humans have chased for two centuries: usable power. How we generate it has changed more in the last twenty years than in the previous hundred.
How oil changed industrialisation
The modern industrial world was built on fossil fuels. Coal powered the first industrial revolution, but it was the rise of oil โ beginning with the first commercial well in Pennsylvania in 1859 โ that reshaped the twentieth century. Cheap, energy-dense and easy to transport, oil gave us kerosene for light, then the internal combustion engine, and with it mass car ownership, aviation, mechanised farming, global shipping, and the petrochemicals behind plastics, fertilisers and medicines. Whole economies and geopolitics reorganised around access to it. Oil made modern industrial life possible โ and, as we now understand, drove the carbon emissions the world is racing to bring down.
The clean-energy turning point
2025 marked a genuine milestone: for the first time in the modern power system, renewables overtook coal in the global electricity mix, together supplying more than a third of the world's electricity. Solar and wind together reached close to a fifth of global generation and are growing faster than any source in history. Global renewable capacity passed 5,100 gigawatts by the end of 2025, with solar alone accounting for more than three-quarters of new additions. In many countries, building new solar is now the cheapest way to make electricity ever recorded โ on average around 40% cheaper than new coal.
Clean energy sources at a glance
| Source | Where it stands | Strengths & limits |
|---|---|---|
| Solar PV | Fastest-growing source; ~2,400 GW installed; leads all new capacity | Cheap and modular, works from a rooftop to a desert farm; variable, needs storage for night |
| Wind | ~1,290 GW installed; offshore expanding fast | High output, strong at night and in winter; needs good sites and grid links |
| Hydropower | Largest single renewable source, ~1,300 GW; ~47% of renewable generation | Reliable, storable, dispatchable; limited by suitable rivers and ecological impact |
| Geothermal & others | Smaller but steady; bioenergy, geothermal, marine | Firm, round-the-clock power; geographically limited |
| Nuclear | Not renewable but low-carbon; growing again | Reliable baseload with no direct emissions; high upfront cost and long build |
The impact of hydropower
Hydropower is the quiet giant of clean energy โ the largest renewable source of electricity on Earth and the backbone of grids from Norway to Brazil. Unlike solar and wind, a dam can store energy and release it on demand, making it invaluable for balancing a grid, and pumped-storage hydro provides the vast majority of the world's grid-scale energy storage. China's Three Gorges Dam, at 22.5 gigawatts, is the single largest power station of any kind ever built. Hydropower's limits are physical and ecological: the best river sites are largely taken, and large dams can displace communities and disrupt ecosystems, so much of today's growth comes from upgrading existing plants rather than building new mega-dams.
How solar is changing lives
Beyond the giant farms, solar's most human impact is off the grid. In much of sub-Saharan Africa and South Asia, small solar panels and pay-as-you-go home systems are bringing electric light, phone charging and refrigeration to families who never had a grid connection โ often the same leap that mobile money made in banking. In 2025, off-grid solar led a doubling of renewable additions across sub-Saharan Africa, and Pakistan added roughly 10 gigawatts of mostly rooftop and distributed solar in a single year. For a student able to study after dark, a clinic able to keep vaccines cold, or a shop able to stay open in the evening, a single panel can change daily life.
Wind turbines
Modern wind turbines are among the largest moving machines ever built, with blades longer than a football pitch on the biggest offshore models. There are well over a million turbines operating worldwide. Denmark now draws more than 70% of its electricity from wind, the United Kingdom hosts some of the world's largest offshore farms, and the North Sea is becoming a shared clean-energy hub for Europe. Onshore wind is among the cheapest electricity available; offshore costs more but taps stronger, steadier winds and frees up land.
DIY dams & energy videos worth watching
If you like to build, micro-hydro and small-scale renewable projects are a fascinating rabbit hole โ a small stream can genuinely power a cabin. Here are popular, freely available DIY energy videos on YouTube to learn from:
- Amazing DIY Hydropower โ Generating 220V from WaterBuilding a small 220V micro-hydro system on a rural river using simple tools.
- DIY Micro Hydro Part 1 โ Head, Flow & Power CalculationsThe maths first: how head and flow determine how much power you can get.
- The $50 Water Turbine โ DIY, Portable, Open SourceA low-head, low-cost turbine you can drop into a waterway.
- Free Energy from a Stream โ Micro Hydro TurbinesSmall 10โ20 watt converters for remote, off-grid use.
- DIY Hydro Power Generator โ Construction + Field TripFull build and a real-world test in the field.
Global actions to restore the environment
Alongside cleaning up energy, the world is trying to repair the land โ and tree planting is the most visible effort. Progress is real but uneven: planting is easy, keeping trees alive for decades is hard. Here's where the biggest campaigns stand.
| Region / campaign | Scale | Status |
|---|---|---|
| China โ Great Green Wall | ~66 billion trees since 1978; 34 billion more planned by mid-century | Forest cover in the zone rose from 5% to 14%; widely seen as a success, with planted forests growing fast |
| Africa โ Great Green Wall | An 8,000 km belt from Senegal to Djibouti; target to restore 100 million hectares by 2030 | Roughly 15โ18% complete; strong in Ethiopia, Senegal and Niger, struggling in conflict-hit states |
| Ethiopia โ Green Legacy | Billions of seedlings in national planting drives | One of the most ambitious per-capita efforts anywhere |
| Kenya โ Green Belt Movement | 30+ million trees, founded by Nobel laureate Wangari Maathai | The community-led model that inspired much of the global movement |
| Global โ Trillion Tree Campaign | ~14 billion trees registered toward a one-trillion goal | Coordinates projects worldwide alongside the Bonn Challenge |
The honest lesson from these projects is that a tree in the ground is only the start. In many semi-arid restoration areas, fewer than half of planted seedlings survive without years of care, which is why the most successful efforts โ China's disciplined, well-funded programme, or Niger's farmer-managed natural regeneration โ pair planting with long-term maintenance and local ownership rather than one-off planting days.
Electricity demand in the AI era
Here's where energy and technology collide. Training and running artificial intelligence takes enormous computing power, and computing takes electricity. Data centres used roughly 415 terawatt-hours in 2024 โ about 1.5% of the world's electricity โ and the International Energy Agency projects that will roughly double to around 945 TWh by 2030, close to the entire electricity consumption of Japan. AI is the single biggest driver: demand from AI-focused data centres is set to more than quadruple by 2030.
The scale of investment is staggering โ the combined capital spending of the five largest technology companies on data centres now exceeds global investment in oil and gas production. In the United States, data centres used about 4% of national electricity in 2023 and could reach 7โ12% by 2028; in Ireland the figure is already above a fifth. That said, in the global picture data centres are still projected to be under 3% of world electricity by 2030 โ less than the extra demand from electric vehicles or air conditioning. The race now is to power all this new computing with the clean energy the rest of this page describes, rather than with new fossil generation.
Frequently asked questions
What is Ohm's Law?
Ohm's Law says voltage equals current times resistance: V = I ร R. From any two of voltage, current and resistance you can find the third, and power follows as P = V ร I. Use the Ohm's Law tab above to solve for whichever you're missing.
How do I calculate voltage drop on a wire?
For single-phase, voltage drop โ (2 ร K ร I ร L) รท circular mils, where K is about 12.9 for copper or 21.2 for aluminium, I is amps and L is the one-way length in feet. Keep it under about 3% on a branch circuit. The Voltage Drop tab does this by wire size.
What size air conditioner (BTU) do I need?
Roughly 20 BTU per square foot, adjusted up for sunny rooms and extra occupants. A 300 sq ft room needs about 6,000 BTU; divide BTU by 12,000 for the size in tons. The BTU tab applies these adjustments.
What share of the world's electricity is renewable?
In 2025, renewables overtook coal for the first time, supplying more than a third of global electricity. Solar and wind together reached close to 20% and are growing fastest; hydropower is still the largest single renewable source.
How much electricity does AI use?
Data centres used about 415 TWh in 2024 (~1.5% of world electricity). The IEA expects that to roughly double to ~945 TWh by 2030 โ about Japan's total consumption โ with AI the biggest driver.
Which country has planted the most trees?
China leads by scale, with about 66 billion trees planted since 1978 in its Great Green Wall, lifting forest cover in the zone from 5% to 14%. Africa's Great Green Wall and Ethiopia's Green Legacy are other major efforts, though survival depends on long-term care.
More tools
Results are estimates for planning and education only, not a substitute for a licensed electrician or engineer. Follow your local electrical code. Energy statistics reflect 2025โ2026 data and change over time.