Quick reference

Formula library

Each formula with its variables, units and a link to the calculator that uses it. Open a formula for a worked example, when to use it and the most common mistake.

Fabric

  • Fabric GSM

    GSM=WA×10 000\text{GSM} = \dfrac{W}{A} \times 10\,000

    Fabric weight per unit area in grams per square meter, calculated from the weight and area of a cut sample.

    W
    Sample weight (g)
    A
    Sample area (cm²)
    Example and notes Calculator

  • GSM and oz/yd² conversion

    oz/yd2=GSM33.906GSM=oz/yd2×33.906\text{oz/yd}^2 = \dfrac{\text{GSM}}{33.906} \qquad \text{GSM} = \text{oz/yd}^2 \times 33.906

    Converts fabric area weight between grams per square meter and ounces per square yard using the exact factor 33.906.

    GSM
    Area weight (g/m²)
    oz/yd²
    Area weight (ounces per square yard)
    33.906
    Conversion factor (28.3495 g per oz divided by 0.836127 m² per yd²) (-)
    Example and notes Calculator

  • Yarn count conversion

    Tex=590.54Ne=1000Nm=den9=dtex10\text{Tex} = \dfrac{590.54}{N_e} = \dfrac{1000}{N_m} = \dfrac{\text{den}}{9} = \dfrac{\text{dtex}}{10}

    Converts yarn count between the direct systems (tex, dtex, denier) and the indirect systems (Ne, Nm) through tex.

    Tex
    Grams per 1,000 meters (g/km)
    Ne
    English cotton count (840 yd hanks per lb) (-)
    Nm
    Metric count (km per kg) (-)
    den
    Denier (grams per 9,000 m) (-)
    dtex
    Decitex (grams per 10,000 m) (-)
    Example and notes Calculator

  • Woven GSM from construction

    GSM≈39.37[EPI(1+C1)T1+PPI(1+C2)T2]1000\text{GSM} \approx \dfrac{39.37\left[\text{EPI}(1+C_1)T_1 + \text{PPI}(1+C_2)T_2\right]}{1000}

    Estimates woven fabric weight from ends and picks per inch, yarn counts and crimp, before a cut sample is available.

    EPI
    Ends per inch (threads/in)
    PPI
    Picks per inch (threads/in)
    C₁
    Warp crimp as a fraction (-)
    C₂
    Weft crimp as a fraction (-)
    T₁
    Warp count (tex)
    Example and notes Calculator

  • Knit GSM from loop length

    GSM≈CPI×WPI×1550×ℓ×T106\text{GSM} \approx \dfrac{\text{CPI} \times \text{WPI} \times 1550 \times \ell \times T}{10^{6}}

    Estimates single jersey weight from courses and wales per inch, stitch length and yarn count.

    CPI
    Courses per inch (per in)
    WPI
    Wales per inch (per in)
    ℓ
    Stitch (loop) length (mm)
    T
    Yarn count (tex)
    1550
    Square inches per square meter (in²/m²)
    Example and notes Calculator

  • Dimensional change (shrinkage)

    Δ%=La−LbLb×100\Delta\% = \dfrac{L_a - L_b}{L_b} \times 100

    Percentage change in a measured distance after washing or another treatment. Negative values mean shrinkage and positive values mean growth.

    L_b
    Benchmark distance before treatment (cm)
    L_a
    Benchmark distance after treatment (cm)
    Example and notes Calculator

Consumption

  • T-shirt fabric consumption

    kg/dz=(BL+SL+aL)(12C+aW)×2×GSM×12107\text{kg/dz} = \dfrac{(BL + SL + a_L)(\tfrac{1}{2}C + a_W) \times 2 \times \text{GSM} \times 12}{10^{7}}

    Body-block estimate of knit fabric weight per dozen basic T-shirts from body length, sleeve length, half chest, GSM and allowances.

    BL
    Body length (cm)
    SL
    Sleeve length (cm)
    ½C
    Half chest (cm)
    a_L
    Length allowances (hems and seams) (cm)
    a_W
    Width allowances (side seams) (cm)
    Example and notes Calculator

  • Knit consumption by panel area

    W=∑(L×B×q)10 000×GSM×(1+w100)W = \dfrac{\sum (L \times B \times q)}{10\,000} \times \text{GSM} \times \left(1 + \dfrac{w}{100}\right)

    Fabric weight per garment from the area of each pattern panel, the fabric GSM and a wastage allowance. Works for any knit style.

    L
    Panel length with allowances (cm)
    B
    Panel width with allowances (cm)
    q
    Number of that panel per garment (pcs)
    w
    Cutting wastage (%)
    Example and notes Calculator

  • Woven consumption from a marker

    C=Lmn(1+a100)C = \dfrac{L_m}{n}\left(1 + \dfrac{a}{100}\right)

    Fabric length per garment from the marker length, the number of garments in the marker and an end loss allowance.

    L_m
    Marker length (m or yd)
    n
    Garments in the marker (pcs)
    a
    End loss and other allowances (%)
    Example and notes Calculator

  • Marker efficiency

    ηm=ApLm×Wm×100\eta_m = \dfrac{A_p}{L_m \times W_m} \times 100

    The share of the marker area covered by pattern pieces. The rest becomes cutting waste.

    A_p
    Total area of all pattern pieces in the marker (cm²)
    L_m
    Marker length (cm)
    W_m
    Marker width (cm)
    Example and notes Calculator

  • Thread consumption

    T=∑(Si×ri)100(1+w100)T = \dfrac{\sum (S_i \times r_i)}{100}\left(1 + \dfrac{w}{100}\right)

    Sewing thread per garment from each seam length and the measured thread-to-seam ratio of its stitch type, plus wastage.

    S_i
    Seam length for stitch type i (cm)
    r_i
    Thread used per cm of seam for that stitch type (cm/cm)
    w
    Wastage allowance (%)
    Example and notes Calculator

Industrial engineering

  • Standard minute value (SMV)

    SMV=tobs60×R100×(1+A100)\text{SMV} = \dfrac{t_{obs}}{60} \times \dfrac{R}{100} \times \left(1 + \dfrac{A}{100}\right)

    The standard time for an operation or garment in minutes, built from observed time, performance rating and allowances.

    t_obs
    Average observed cycle time (s)
    R
    Performance rating (100 = standard pace) (%)
    A
    Personal, fatigue and delay allowance (%)
    Example and notes Calculator

  • Basic time

    BT=tobs×R100BT = t_{obs} \times \dfrac{R}{100}

    Observed time adjusted by the performance rating, before allowances are added. It is the work content at standard pace.

    t_obs
    Observed time (min or s)
    R
    Performance rating (%)
    Example and notes Calculator

  • Line efficiency

    η=P×SMVM×T×100\eta = \dfrac{P \times \text{SMV}}{M \times T} \times 100

    Earned minutes (good output × SMV) as a percentage of available minutes (manpower × working minutes).

    P
    Good output (pcs)
    SMV
    Garment SMV (min)
    M
    Manpower counted in the line (persons)
    T
    Working minutes per person (min)
    Example and notes Calculator

  • Manpower requirement

    M=Q×SMVT×η×11−aM = \dfrac{Q \times \text{SMV}}{T \times \eta} \times \dfrac{1}{1-a}

    Operators needed to meet a daily target at a planned efficiency, grossed up for absenteeism.

    Q
    Daily target (pcs)
    T
    Working minutes per day (min)
    η
    Planned efficiency (-)
    a
    Absenteeism (-)
    Example and notes Calculator

  • Machine requirement

    Nop=Q×SMVopT×ηN_{op} = \dfrac{Q \times \text{SMV}_{op}}{T \times \eta}

    Machines needed for each operation to meet a daily target, rounded up per operation and grouped by machine type.

    Q
    Daily target (pcs)
    SMV_op
    Operation SMV (min)
    T
    Working minutes (min)
    η
    Planned efficiency (-)
    Example and notes Calculator

  • Takt time

    Takt=Available production timeCustomer demand\text{Takt} = \dfrac{\text{Available production time}}{\text{Customer demand}}

    The pace of customer demand. One unit must be completed every takt interval to meet demand in the available time.

    Available time
    Planned working time minus planned breaks (s)
    Demand
    Units required in the same period (pcs)
    Example and notes Calculator

  • Pitch time

    Pitchline=SMVgarmentNPitchlean=Takt×q\text{Pitch}_{line} = \dfrac{\text{SMV}_{garment}}{N} \qquad \text{Pitch}_{lean} = \text{Takt} \times q

    In garment line balancing, the ideal work content per operator (garment SMV / operators). In lean practice, takt time × pack-out quantity.

    SMV_garment
    Total garment SMV (min)
    N
    Operators in the line (persons)
    q
    Pack-out quantity (pcs)
    Example and notes Calculator

  • Line balancing efficiency

    ηLB=∑tin×tmax×100\eta_{LB} = \dfrac{\sum t_i}{n \times t_{max}} \times 100

    How evenly work is spread across stations. Total work content divided by stations × bottleneck station time.

    t_i
    Work content of station i (min)
    n
    Number of stations (-)
    t_max
    Time of the slowest (bottleneck) station (min)
    Example and notes Calculator

  • Overall Equipment Effectiveness (OEE)

    OEE=A×P×Q\text{OEE} = A \times P \times Q

    The product of availability, performance and quality. It shows how much of planned time produced good output at ideal speed.

    A
    Availability: run time / planned production time (-)
    P
    Performance: (ideal cycle time × total count) / run time (-)
    Q
    Quality: good count / total count (-)
    Example and notes Calculator

Production

  • Production target

    Target=M×T×ηSMV\text{Target} = \dfrac{M \times T \times \eta}{\text{SMV}}

    The number of pieces a line should produce in a period at a planned efficiency.

    M
    Manpower (persons)
    T
    Working minutes (min)
    η
    Planned efficiency as a fraction (-)
    SMV
    Garment SMV (min)
    Example and notes Calculator

  • Production capacity

    Cpcs=L×O×(1−a)×H×60×D×ηSMVC_{pcs} = \dfrac{L \times O \times (1-a) \times H \times 60 \times D \times \eta}{\text{SMV}}

    Sewing capacity for a period in minutes and pieces, after absenteeism and efficiency.

    L
    Lines (-)
    O
    Operators per line (persons)
    a
    Absenteeism as a fraction (-)
    H
    Working hours per day (h)
    D
    Working days in the period (days)
    Example and notes Calculator

  • Machine utilization

    U=truntavailable×100U = \dfrac{t_{run}}{t_{available}} \times 100

    The share of available time that a machine was actually running production.

    t_run
    Time the machine was producing (min)
    t_available
    Time it was scheduled to be available (min)
    Example and notes Calculator

  • Machine productivity

    Productivitym=PNm×H\text{Productivity}_m = \dfrac{P}{N_m \times H}

    Output per machine hour. Useful for machine-paced processes where the machine, not the operator, sets the pace.

    P
    Good output (pcs or kg)
    N_m
    Number of machines (-)
    H
    Running hours per machine (h)
    Example and notes Calculator

Workforce

  • Operator efficiency

    ηop=n×SMVopTworked×100\eta_{op} = \dfrac{n \times \text{SMV}_{op}}{T_{worked}} \times 100

    One operator's earned minutes (pieces × operation SMV) as a percentage of the minutes they worked on that operation.

    n
    Good pieces completed (pcs)
    SMV_op
    SMV of the operation (min)
    T_worked
    Minutes worked on the operation (min)
    Example and notes Calculator

  • Operator capacity per hour

    C100=60SMVopCobs=3600tcycleC_{100} = \dfrac{60}{\text{SMV}_{op}} \qquad C_{obs} = \dfrac{3600}{t_{cycle}}

    The number of pieces one operator can make in an hour on an operation, at 100% or from a measured cycle time.

    SMV_op
    Operation SMV (min)
    t_cycle
    Average observed cycle time (s)
    Example and notes Calculator

  • Absenteeism rate

    Absenteeism=dabsentdscheduled×100\text{Absenteeism} = \dfrac{d_{absent}}{d_{scheduled}} \times 100

    Person-days lost to absence as a percentage of person-days scheduled.

    d_absent
    Person-days absent (days)
    d_scheduled
    Person-days scheduled (days)
    Example and notes Calculator

  • Labour productivity

    Productivity=PM\text{Productivity} = \dfrac{P}{M}

    Output per operator per day (or per hour). Simple to count, but only comparable between lines making similar products.

    P
    Good output in the period (pcs)
    M
    Manpower (persons)
    Example and notes Calculator

Quality

  • DHU (defects per hundred units)

    DHU=DU×100\text{DHU} = \dfrac{D}{U} \times 100

    Total defects found per 100 units inspected. One unit can carry several defects, so DHU can exceed 100.

    D
    Total defects found (defects)
    U
    Units inspected (pcs)
    Example and notes Calculator

  • Defective percentage

    % defective=UdU×100\% \text{ defective} = \dfrac{U_d}{U} \times 100

    The share of inspected units that have at least one defect. Each unit is counted once, however many defects it has.

    U_d
    Units with one or more defects (pcs)
    U
    Units inspected (pcs)
    Example and notes Calculator

  • Right First Time (RFT)

    RFT=UpassUchecked×100\text{RFT} = \dfrac{U_{pass}}{U_{checked}} \times 100

    The percentage of units that pass inspection the first time, without any repair or rework.

    U_pass
    Units accepted at first check with no repair (pcs)
    U_checked
    Units checked (pcs)
    Example and notes Calculator

  • Rejection percentage

    % rejection=UrejUprod×100\% \text{ rejection} = \dfrac{U_{rej}}{U_{prod}} \times 100

    The share of produced units rejected as not saleable (not repairable to specification).

    U_rej
    Units rejected as not repairable (pcs)
    U_prod
    Units produced (pcs)
    Example and notes Calculator

  • Four-point system score

    P100=Total points×3600Y×WP_{100} = \dfrac{\text{Total points} \times 3600}{Y \times W}

    Fabric defect penalty points normalised to 100 square yards, so rolls of different length and width can be compared.

    Total points
    Sum of 1 to 4 point penalties for the roll (points)
    Y
    Length inspected (yd)
    W
    Cuttable width (in)
    3600
    36 in per yd × 100 sq yd (-)
    Example and notes Calculator

Costing

  • Cost per minute (CPM)

    CPM=CmonthN×T×D\text{CPM} = \dfrac{C_{month}}{N \times T \times D}

    The factory's manufacturing cost for one available minute of sewing capacity. The basis of CM costing.

    C_month
    Monthly manufacturing cost (currency)
    N
    Operators (persons)
    T
    Minutes per day (min)
    D
    Working days per month (days)
    Example and notes Calculator

  • CM cost (cost of making)

    CMpc=SMV×CPMη\text{CM}_{pc} = \dfrac{\text{SMV} \times \text{CPM}}{\eta}

    The cost of cutting, sewing and finishing one garment, from its SMV, the cost per minute and the expected efficiency.

    SMV
    Garment SMV (min)
    CPM
    Cost per available minute (currency/min)
    η
    Expected efficiency as a fraction (-)
    Example and notes Calculator

  • FOB price build-up

    FOB=(F+T+CM+O)(1+c100)(1+p100)\text{FOB} = (F + T + \text{CM} + O)\left(1+\dfrac{c}{100}\right)\left(1+\dfrac{p}{100}\right)

    Garment price at the FOB point built from fabric, trims, CM and other processes, plus commercial cost and profit.

    F
    Fabric cost per piece (currency)
    T
    Trims and accessories per piece (currency)
    CM
    Cost of making per piece (currency)
    O
    Other processes (wash, print, embroidery, testing) (currency)
    c
    Commercial cost (%)
    Example and notes Calculator