Air Conditioning
Multi-Room AC Sizing Calculator
Total cooling load across several rooms
Updated July 12, 2026 · Live
What this tool does
Adds up the cooling load across up to four rooms and suggests whether a single split or a multi-split system suits.
Enter the floor area of up to four rooms; the calculator returns the total cooling load in kW and BTU/h.
People also use
Formula Used
Adds up the cooling load across up to four rooms and suggests whether a single split or a multi-split system suits. It runs entirely in your browser and shows the working, so you can check every step against your own figures.
How the multi-room ac sizing calculator works
Each room’s cooling load is its floor area times the base rate per m². The tool sums the rooms you enter for a total in kW and BTU/h, and shows the largest single zone. Above one room, a multi-split — one outdoor unit feeding several indoor heads — usually suits better than separate single units.
What you enter
Enter the floor area of up to four rooms; the calculator returns the total cooling load in kW and BTU/h. Every field is editable, and the result recalculates the moment you change a value.
Reading the result
The total sizes the outdoor unit; the largest zone helps pick the biggest indoor head. Diversity means the peak total is rarely the simple sum, so a multi-split outdoor unit can often be a little smaller than the added-up figure.
Safe by design
This tool sizes the cooling load and running cost only. Refrigerant handling and the electrical connection are regulated work for a qualified F-Gas and electrical engineer.
Assumptions and limits
This uses a flat per-m² rate for each room and ignores glazing, occupancy and orientation differences between rooms. For a precise multi-split design, size each room with the single-room tool and apply a diversity factor to the outdoor unit.
Using it with the rest of BuildMetricLab
This calculator is one step in planning the job. Pair it with the related tools in this category and across BuildMetricLab to go from a single figure to a full costed plan — a sizing figure feeds a cost estimate, a cost estimate feeds a project budget, and each result carries straight into the next tool. Every BuildMetricLab tool runs entirely in your browser — no sign-up, nothing sent to a server, and the formula is shown on the page so the maths can be audited.
Sources & methodology
Adds up the cooling load across up to four rooms and suggests whether a single split or a multi-split system suits. Every result is calculated from the values you enter, all inputs are editable, and no time-sensitive prices or rates are embedded.
Frequently asked questions
Single split or multi-split?
One room suits a single split; several rooms usually suit a multi-split — one outdoor unit feeding several indoor heads — which is neater and cheaper than many singles.
Do I add the room loads directly?
For a first estimate, yes. In practice a diversity factor applies because rooms rarely peak together, so the outdoor unit can be a little smaller.
Why size the largest zone?
The biggest room sets the largest indoor head and often the pipe run, so it is worth seeing separately.
Does this account for glazing per room?
No — it uses a flat per-m² rate. For rooms with very different glazing or orientation, size each with the single-room tool.
Spotted something off?
Calculations or display — let us know.