Line of Balance Scheduling: Method, Formula and Example

When the same work repeats floor after floor or kilometre after kilometre, a bar chart hides the thing that matters most: whether each trade is moving at the same speed as the one in front.

When to use line of balance

• High-rise buildings with typical floors
• Housing developments with many similar units
• Linear projects: roads, rail, pipelines, tunnels
• Fit-out of repeated rooms such as hotel rooms or hospital wards

It suits work where the same sequence of activities repeats across many locations. For one-off, highly varied work, a CPM network schedule is usually the better tool.

How to read a line of balance chart

• Each line is one activity, such as formwork, MEP rough-in or drywall.
• The slope is the production rate. A steeper line (on a chart with units on the vertical axis) means more units per day.
• The horizontal gap between lines is the time buffer between one trade finishing a unit and the next trade starting it.
• Converging lines are a warning. A fast trade catching up with a slower trade ahead of it will run out of work and have to stop.
• Diverging lines mean a slower trade is falling further behind, stretching the project.

Line of balance formulas

For one activity, let n = number of units, R = required production rate (units per day), and d = duration for one crew to complete one unit (days).

• Crews needed = R × d (rounded up to a whole crew)
• Actual rate with c crews = c ÷ d units per day
• Time from start of the first unit to finish of the last unit = (n − 1) ÷ R + d

Worked example

A 20-floor building. The target is to complete one floor of drywall every 2 days, so R = 0.5 floors per day. One drywall crew takes 4 days per floor, so d = 4.

1. Crews needed = 0.5 × 4 = 2 crews.
2. Actual rate = 2 ÷ 4 = 0.5 floors per day, which matches the target.
3. Activity duration = (20 − 1) ÷ 0.5 + 4 = 38 + 4 = 42 days from starting floor 1 to finishing floor 20.

If the trade before drywall runs at 0.4 floors per day, the two lines converge, and drywall will catch up and stall. You either slow drywall to match (fewer crews), speed up the trade ahead, or start drywall later with a bigger buffer so the lines don't meet before the last floor.

How to build a line of balance schedule

1. Define the repeating unit and the sequence of activities within it.
2. Estimate the duration per unit for each activity with one crew.
3. Set the target rate, usually from the handover date or the slowest critical activity.
4. Calculate crews for each activity to match the target rate as closely as possible.
5. Add buffers between activities, in time or in units, to absorb variation.
6. Plot the lines and check for convergence.
7. Track actual progress by plotting actual completion of each unit against the plan.

Common mistakes

• Ignoring the learning curve. Early units usually take longer than later ones.
• No buffers, so one slow unit stops every trade behind it.
• Treating non-typical units as typical, such as ground floors, plant floors or roof levels.
• Tracking progress from reports alone. The chart is only as accurate as the "unit complete" data behind it.

Where SpatialSense fits

SpatialSense doesn't build or calculate line of balance schedules. Where it can help is the actual-progress data. A regular 360° walk or scan of each floor or section, timestamped when it's added to a project, shows which units are really complete on a given date, so the actual lines on the chart come from evidence rather than verbal updates. Comparing two dated captures side by side shows what moved between updates.

Frequently asked questions