LED Strip Cutting Calculator

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Table of contents

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

Safe cut length: The final strip length at a valid cut mark, shown in the same unit as Space to cover.

Distance between cut marks: The repeat length from one safe cut line to the next on the LED strip.

Fit choice: The rule used to pick the cut mark: stay under the space, choose the closest mark, or go at least as long as the space.

How the cut fits: The signed difference between the safe cut length and the space to cover. Positive means longer. Negative means shorter.

Cut mark count from the start: The number of cut-spacing intervals to count from the starting end before cutting.

Extra power room (percent): Spare power capacity added to the estimated strip watts when sizing a power supply.

Mistake: Using the strip length you wish existed for Distance between cut marks .
Fix: Use the actual spacing between safe cut marks from the product specs or by measuring mark to mark.

Mistake: Picking the wrong Fit choice for a tight channel or cabinet edge.
Fix: Use Do not go over if extra strip cannot fit; use At least this long only when extra length is acceptable.

Mistake: Mixing Space to cover in feet with Length unit set to inches.
Fix: Check both Length unit and Cut spacing unit before trusting the Safe cut length .

Mistake: Treating a negative How the cut fits value as an error.
Fix: Read the sign: negative means the cut strip is short by that amount, and positive means it is long by that amount.

Mistake: Entering Strip power (watts per foot) but leaving Strip voltage (V) blank or zero.
Fix: Enter the voltage printed on the strip or power supply so the amp estimates can be calculated.

Mistake: Ignoring a negative Strip left after this cut value.
Fix: A negative leftover means the Available strip on hand is not long enough for the planned cut.

• The result assumes the strip can be cut at evenly spaced safe cut marks. If your strip has mixed spacing, use the exact spacing for the section you plan to cut.
• The calculator does not tell you where solder pads, connectors, waterproof coating, or diffuser hardware will land. Check the physical strip before cutting.
• Power results use the entered Strip power (watts per foot) times the cut length. Real power can vary by LED type, brightness setting, controller losses, and supply voltage drop.
• Suggested power supply rating is a planning estimate, not a product approval. Follow the strip maker's instructions if they require a larger margin.
• A Safe cut length of 0 can happen when Fit choice is Do not go over and the space is shorter than one cut interval.
• The calculator rounds to a cut mark mathematically. It cannot confirm that the printed mark is undamaged or that cutting will preserve warranty coverage.

How the cut mark is chosen

LED strips should be cut only at designated cut points, so the calculator converts your lengths to meters and then rounds to a valid cut interval instead of any exact length [1].

meters = value * unit_factor

The unit factors are 0.0254 meter per inch, 0.3048 meter per foot, 0.001 meter per millimeter, 0.01 meter per centimeter, and 1 meter per meter.

ratio = desired_m / spacing_m

k = floor(ratio) for Do not go over

k = round(ratio) for Closest length, with exact halfway ties going shorter

k = ceil(ratio) for At least this long

The interval count k is the Cut mark count from the start.

Length and fit results

cut_m = k * spacing_m

fit_m = cut_m - desired_m

The calculator shows Safe cut length and How the cut fits in the selected Length unit. The fit is signed because the sign matters: positive is extra length, and negative is a short strip.

Optional strip and power results

left_m = available_m - cut_m

cut_ft = cut_m / 0.3048

strip_watts = cut_ft * watts_per_ft

suggested_watts = strip_watts * (1 + headroom_percent / 100)

current_amps = strip_watts / voltage

suggested_current_amps = suggested_watts / voltage

Optional power results appear only when the needed power inputs are valid. Current in amps is calculated from watts divided by volts, which is the same watt relationship rearranged from P = V * I.

Mini-example

If the space is 7.1 ft, the cut spacing is 4 in, and Fit choice is At least this long, the spacing is 0.333333 ft. The ratio is 7.1 / 0.333333, so the calculator rounds up to 22 intervals. The safe cut length is 7.333333 ft, and the fit amount is +0.233333 ft.