Cable Length Calculator
Estimate the total cable length to buy for a run from the straight-line distance plus a slack allowance for corners and connections.
ft
%
Extra for corners, drops, and connections — 10-15% is typical
Cable Length to Buy
86.3 ft
Includes 11.3 ft of slack allowance
How to Estimate Total Cable Length
Measure (or estimate) the straight-line distance between where your cable starts and where it ends, then add a slack allowance to cover the fact that real cable runs are never perfectly straight — they go around corners, drop down walls, loop through conduit, and need a little extra at each end to actually reach the connector or terminal. This calculator adds that allowance as a percentage of the straight-line distance to give you a practical amount to buy.
Buying a bit extra cable is far cheaper than running short mid-job and having to make a second trip to the store — a small roll of spare cable costs a lot less than your time.
Example
A run measuring 75 ft in a straight line, with a 15% slack allowance for corners and connections, needs 75 × 1.15 = 86.25 ft of cable — round up to the nearest standard length when buying.
Common Use Cases
- Estimating how much network, speaker, or extension cable to buy for a room-to-room run.
- Planning cable purchases for a home theater, security camera, or networking installation.
- Budgeting cable length for a job before visiting the hardware store.
FAQs
How is this different from a wire gauge calculator?
This tool estimates how much total cable length to buy for a run. It doesn't determine what thickness (gauge) of wire you need for safety and voltage drop — for that, use our Wire Size Calculator, which sizes AWG gauge based on current and voltage drop over a given run length.
How much slack allowance should I use?
10-15% covers most straightforward runs with a few corners. Runs with many bends, obstacles, or where you need extra service loop at equipment racks may warrant 20% or more.
Should I round up the final number?
Yes — cable is typically sold in fixed roll or spool lengths, so round the calculated total up to the next available length rather than trying to buy an exact fractional amount.