LED Strip Length Calculator

Related Calculators

Table of contents

• How to use
• Common mistakes
• Definitions
• Methodology
• Limitations & assumptions
• Sources

Measured lighting path: The length of wall, shelf, ceiling line, or other route before adding slack or cut-point rounding.

Extra slack: Extra strip length added for corners, connector trimming, small measuring errors, or a little working room.

Cut spacing: The distance between allowed cut marks on the LED strip. The calculator rounds up to the next cut point.

Roll length: The amount of strip in one roll you plan to buy.

Strip power: The power used by the strip at full brightness, entered as watts per ft.

Power supply safety margin: Extra capacity added above the exact strip power when sizing the power supply.

Estimated current: Electrical current in amps, found from strip watts divided by strip voltage.

Max length from one feed: A product-specific length limit for powering one strip section from one end.

Mistake: Entering the full room perimeter in Measured path length while What are you measuring? is still set to Rectangular room.
Fix: Use Room length, Room width, and Room walls to light for room mode, or switch What are you measuring? to Straight measured run.

Mistake: Typing a meters-per-roll value into Roll length as if it were feet.
Fix: Enter Roll length in ft, using the length printed on the product box or listing after converting if needed.

Mistake: Putting watts per meter into Strip power, which expects W/ft.
Fix: Convert the product's power rating to watts per ft before entering Strip power.

Mistake: Leaving Cut spacing at the default when your strip has different cut marks.
Fix: Enter the actual Cut spacing in inches so LED strip length to plan for rounds up to a real cut point.

Mistake: Choosing a Power supply safety margin that is blank or negative.
Fix: Enter 0 percent or more for Power supply safety margin; many users choose a positive margin so the supply is not planned at its exact limit.

Mistake: Treating Feed sections to consider as an electrical design approval.
Fix: Use Max length from one feed only as a planning check, then follow the strip maker's wiring instructions for the actual feed points.

• The calculator estimates strip purchasing length and basic power needs. It does not choose wire gauge, fuse size, controller type, dimmer type, or code-compliant installation details.
• Room mode assumes a rectangle and straight wall runs. Alcoves, diagonal paths, door gaps, cabinets, curved paths, and corner connector lengths need manual adjustment through Extra slack or separate measurements.
• Cut rounding uses one Cut spacing value for the whole project. Mixed strips or sections with different cut marks should be calculated separately.
• Strip power at full brightness depends on the exact product and color setting. If the entered Strip power is too low, Recommended power supply size and Estimated current will also be too low.
• Feed sections to consider is shown only when Max length from one feed is entered. It is a planning prompt, not a guarantee that voltage drop, heat, or brightness will be acceptable.
• Rolls to buy assumes you buy whole rolls of one Roll length and can use the strip across the planned sections. Some strips, waterproof sleeves, connectors, or warranty rules may limit how leftover pieces can be used.

How the length is found

For a rectangular room, the calculator first sorts the two room sides into a long side and a short side, then uses the Room walls to light choice to find Measured lighting path.

All 4 walls: base_length_ft = 2 * (L + W)

Two long walls: base_length_ft = 2 * max(L, W)

Two short walls: base_length_ft = 2 * min(L, W)

One long wall: base_length_ft = max(L, W)

One short wall: base_length_ft = min(L, W)

Three walls, skip one long wall: base_length_ft = max(L, W) + 2 * min(L, W)

Three walls, skip one short wall: base_length_ft = 2 * max(L, W) + min(L, W)

For a straight run, the measured path is used directly.

base_length_ft = path_length_ft

Cut points, rolls, and leftover strip

The calculator adds Extra slack, converts Cut spacing from inches to feet, then rounds up. It rounds up because cutting shorter than the needed path may leave the strip too short.

cut_spacing_ft = cut_spacing_in / 12

raw_needed_ft = base_length_ft + extra_slack_ft

adjusted_length_ft = ceil(raw_needed_ft / cut_spacing_ft) * cut_spacing_ft

Whole-roll buying is then estimated from Roll length.

rolls_needed = ceil(adjusted_length_ft / roll_length_ft)

leftover_length_ft = rolls_needed * roll_length_ft - adjusted_length_ft

Power, current, and feed sections

Strip power at full brightness is the planned strip length times Strip power. Recommended power supply size adds the Power supply safety margin. Estimated current uses the watt relation P = V * I, rearranged as current = watts / volts.

total_strip_power_w = adjusted_length_ft * watts_per_ft

recommended_power_supply_w = total_strip_power_w * (1 + power_margin_percent / 100)

current_a = total_strip_power_w / strip_voltage_v

If Max length from one feed is entered, the calculator divides the adjusted length into the fewest whole feed sections to consider.

feed_sections_needed = ceil(adjusted_length_ft / max_one_end_feed_ft)

Worked example

A 12 ft by 10 ft room with all 4 walls lit has a measured path of 2 * (12 + 10) = 44 ft. With 1 ft of slack and 2 inch cut spacing, the raw need is 45 ft, which already lands on a cut point, so LED strip length to plan for is 45 ft. With 16.4 ft rolls, Rolls to buy is ceil(45 / 16.4) = 3, and Estimated leftover strip is 3 * 16.4 - 45 = 4.2 ft. At 4.4 W/ft, Strip power at full brightness is 198 W. With a 20 percent margin, Recommended power supply size is 237.6 W. At 12 V, Estimated current is 16.5 A. If Max length from one feed is 16 ft, Feed sections to consider is ceil(45 / 16) = 3.