Factorio Nuclear Reactor Calculator for Reactors, Turbines and Pumps
Use this Factorio nuclear reactor calculator before building a 2x2, 2x4 or larger reactor block. Enter the reactor grid, power target and safety margin to estimate neighbor bonus heat output, heat exchangers, steam turbines, offshore pumps, water flow and uranium fuel-cell demand.
Last updated: June 23, 2026. Built for Factorio 2.0 and Space Age nuclear planning.
Factorio Nuclear Reactor Calculator Tool
Set the reactor rows and columns, then compare the heat output with your target MW. The calculator uses the standard reactor neighbor bonus model: each reactor provides 40 MW, and each touching reactor pair adds 80 MW of extra heat to the whole block.
Estimated nuclear block output
Inputs to verify before copying the result
- Reactor grid: rows x columns, such as 2x2, 2x4 or 2x6.
- Target MW: the factory demand you want this nuclear block to cover.
- Safety margin: extra capacity for lasers, roboports, beacons and expansion.
- Heat exchanger and turbine ratios: keep defaults unless a mod changes item data.
- Water and fuel logistics: one offshore pump supports about 1200 water per second.
Quick Answer: The Nuclear Ratio Behind the Calculator
A common 2x2 nuclear block has 4 reactors, 4 neighbor pairs and 480 MW of heat output. That usually means 48 heat exchangers, about 83 steam turbines, roughly 4944 water per second and 5 offshore pumps before layout losses.
- Base output is 40 MW per reactor.
- Each touching reactor pair adds 80 MW of bonus heat to the reactor block.
- Heat exchangers consume about 10 MW of heat and 103 water per second each.
- Steam turbines produce about 5.82 MW each, so turbine counts rarely divide evenly.
- Round exchangers, turbines and pumps up, then leave space for pipes and heat-pipe reach.
Factorio Nuclear Reactor Formula
The calculator is intentionally transparent so you can check the math against your blueprint instead of trusting a black-box number.
| Calculation | Formula | Why it matters |
|---|---|---|
| Reactors | rows x columns | Determines fuel-cell use and base heat output. |
| Neighbor pairs | rows x (columns - 1) + columns x (rows - 1) | Each touching pair increases total reactor output. |
| Heat output | reactors x 40 MW + neighbor pairs x 80 MW | This is the MW budget for heat exchangers and turbines. |
| Heat exchangers | ceil(heat output / 10) | Too few exchangers wastes reactor heat. |
| Steam turbines | ceil(heat output / 5.82) | Round up because turbine output does not divide cleanly. |
| Fuel cells | reactors x 0.3 cells per minute | Keeps uranium processing and spent-cell handling sized correctly. |
How to Use the Nuclear Reactor Calculator
Choose the reactor block size
Start with the physical design you can build: 2x2 for a compact first nuclear plant, 2x4 or larger for late-game power.
Enter the target MW
Use the in-game power graph or a production plan to estimate demand. Include the next factory block, not only current consumption.
Set a safety margin
A 20 percent margin is a reasonable starting point. Use more if laser defenses, bots, beacons or expansion spikes are common.
Build support pieces first
Place water, pumps, heat exchangers and turbines so they can actually consume the reactor heat.
Watch the live power graph
After startup, verify satisfaction, steam buffers and fuel-cell rhythm. A ratio that works on paper can still fail from pipe or heat layout.
Common Nuclear Calculator Examples
2x2 starter nuclear block
The familiar 2x2 layout outputs 480 MW before practical losses. It is large enough for many mid-game factories and simple enough to blueprint.
2x4 expansion block
A 2x4 layout has more neighbor pairs, so its output scales better than two isolated 2x2 plants. Check water and turbine space carefully.
Single-reactor emergency setup
A single reactor has no neighbor bonus, so it outputs only 40 MW. It is useful for learning but inefficient for sustained factory power.
Power target sanity check
If the margin status shows a shortfall, do not rely on accumulators to hide it forever. Add reactor capacity or reduce the planned load.
Nuclear Planning Edge Cases
Most nuclear mistakes are layout mistakes rather than formula mistakes. Use the output numbers as a minimum bill of materials, then check the build in game.
| Case | Risk | What to verify |
|---|---|---|
| Too few offshore pumps | Exchangers cannot make enough steam even if reactor heat is available. | Give every exchanger bank reliable water and avoid pipe bottlenecks. |
| Long heat-pipe runs | Distant exchangers may warm up slowly or underperform. | Keep heat exchangers close enough to the reactor block and test startup. |
| No fuel-cell control | Reactors can consume fuel while steam storage is already full. | Use circuit control if you want to reduce uranium waste. |
| Spent fuel cells ignored | Output slots fill up and stop the reactor cycle. | Remove spent cells and route them to reprocessing. |
| Target MW equals average demand | Power dips during spikes, laser use or bot charging. | Add a safety margin and accumulator buffer. |
Need full factory demand before sizing nuclear?
Use the main Factorio calculator to estimate production and power demand, then return here to size the nuclear block that will support it.
Factorio Nuclear Reactor Calculator FAQ
What is the 2x2 nuclear reactor ratio in Factorio?
A 2x2 reactor block outputs 480 MW of heat. A practical support plan is 48 heat exchangers, about 83 steam turbines and 5 offshore pumps, then rounded and adjusted for layout.
How does the reactor neighbor bonus work?
Each reactor provides 40 MW by itself. Every touching reactor pair adds 80 MW of bonus heat to the reactor block, which is why compact multi-reactor designs are much stronger than isolated reactors.
How many steam turbines per heat exchanger do I need?
One heat exchanger supports roughly 10 MW, and one steam turbine produces about 5.82 MW. That means the ratio is about 1.72 turbines per exchanger, so you normally round turbine counts up.
How many offshore pumps does nuclear power need?
Each heat exchanger consumes about 103 water per second, and an offshore pump supplies 1200 water per second. Divide total exchanger water demand by 1200 and round up.
Does this calculator replace testing a nuclear blueprint?
No. It sizes the main ratios, but your actual blueprint must still handle heat-pipe distance, pipe throughput, water placement, fuel insertion, spent-cell removal and startup behavior.
Sources and Further Reading
These references help verify nuclear power item behavior and ratios.