Calculate how much main fabric and lining you need for flat Roman blinds. Get cut dimensions, a width check, cutting rows and separate purchase lengths in metres or yards.
How much fabric do I need for a Roman blind?
For a flat Roman blind, start with the finished blind width and drop. Add the actual fabric consumed by the side turns, top attachment and bottom hem. Check whether that cutting width fits the usable fabric width. Calculate the lining separately because its size, allowances and rod pockets can differ from the main fabric.
The calculator above makes that material plan for one blind or a batch of identical blinds. It shows the dimensions of every type of cut panel, how many panels fit across the roll, the number of cutting rows and the length to buy. The starting values are an editable example. They are not a universal Roman blind pattern.
Choose the finished size before adding allowances
Finished width and drop describe the fabric blind when lowered. A window opening, a headrail width and a finished fabric width are not always the same measurement. First choose your headrail and mounting position. Use its instructions to determine any clearance inside a recess or overlap outside it. Then enter the intended finished fabric size here.
For several different window sizes, calculate each size separately and plan any shared cutting layout before ordering. The quantity box is for identical blinds. Roman blinds do not use the fullness multiplier applied to gathered curtains.
Main fabric formula
Let W be finished width and D be finished drop. Let S be the total fabric allowance at each side, T the total top allowance and B the total bottom allowance.
- Main fabric cut width = W + 2 × S.
- Main fabric cut drop = D + T + B.
An allowance is the total raw cloth consumed by that edge. If an edge is folded twice by 2.5 cm, its total allowance is 5 cm. Do not enter 2.5 cm and expect the calculator to double it again. Include the fabric needed for your attachment or bottom-bar casing within the appropriate total.
Sew Helpful's main-fabric planning guide separates the panel cut drop from extra cloth for trimming and pattern placement. Here, the end allowance and pattern-placement fields serve those purposes. Their values remain yours to check for your construction.
Lining and rod-pocket allowance
This tool assumes a separate lining whose finished top aligns with the finished blind top. If the lining is set in by I at each side and J at the bottom, its finished width is W − 2I and its finished drop is D − J. These are finished insets, not seam allowances.
- Lining cut width = W − 2I + 2 × lining side allowance.
- Lining cut drop = D − J + lining top allowance + lining bottom allowance + pocket allowance.
- For pockets folded into the lining, pocket allowance = number of pockets × 2 × folded pocket depth.
- For separate rod-pocket tape, pocket allowance in the lining is zero.
A folded pocket uses cloth on both sides of its fold. A 1 cm folded depth therefore consumes 2 cm of lining length. This is fabric take-up, not a rod-diameter recommendation. Pocket count, pocket depth, rod spacing and the bottom-bar casing must come from your sewing method. Do not count the same casing again in both a hem and a pocket allowance.
Sew Helpful's lining guide also distinguishes pockets made from lining from separate pocket tape. This calculator estimates the lining material; it does not calculate how much tape, rod, cord or headrail hardware to buy.
What if the fabric is too narrow?
The default requires each main or lining piece to fit without a vertical join. If either cut width is too large after width shrinkage, the calculator asks you to use wider fabric or change the construction. It does not silently turn the blind sideways.
If you choose vertical joins, the calculator divides the required width into equal-width panels. Each join consumes one seam allowance from each of the two meeting panels. The cut strip width is (required assembled cut width + 2 × joining allowance × number of joins) ÷ number of panels.
For example, an assembled cut width of 190 cm with two panels and 1.5 cm joining allowance needs two strips of (190 + 3) ÷ 2 = 96.5 cm. After joining, their combined width is 190 cm. Any side-turn allowances already included in that assembled width still have to be sewn.
This is a plain-fabric material plan. It can create a centre seam, which you may not want. A full centre panel with balanced side panels, a centred motif or matched joins needs a different cutting layout. Confirm that your lining and its coating can be sewn as planned.
Example: two 100 × 150 cm Roman blinds
Use two identical flat blinds, 140 cm usable rolls, no shrinkage and no pattern extra. For the main fabric, choose 5 cm at each side, 5 cm at the top and 10 cm at the bottom. Each main piece is 110 × 165 cm. One fits across the roll, so two pieces need 330 cm.
Set the lining in 2 cm at each side and 2 cm at the bottom. Add 2 cm lining side allowances, 5 cm at the top and 6 cm at the bottom. Four pockets with a folded depth of 1 cm add 8 cm. Each lining piece is 100 × 167 cm, and two need 334 cm.
- Main fabric: (330 + 6) × 1.05 = 352.8 cm. Rounded up in 0.1 m steps, buy 3.6 m.
- Lining: (334 + 6) × 1.05 = 357 cm. Rounded up in 0.1 m steps, buy 3.6 m.
- At illustrative prices of €20/m and €8/m, the combined fabric cost is €100.80.
The example button fills these values. With separate pocket tape instead, the lining cut drop becomes 159 cm and the same purchase settings give 3.5 m of lining. The tape itself is a separate item.
Width, shrinkage and purchase rounding
Enter usable width without selvedges or damaged edges. Width available after shrinkage = entered width × (1 − width shrinkage ÷ 100). The tool checks that width before working out how many whole panels fit across it.
For each material, the length before shrinking is (row cutting length + pattern-placement extra + total end allowance) × (1 + reserve ÷ 100) ÷ (1 − length shrinkage ÷ 100). It then rounds up to the seller's increment. Main fabric and lining are rounded separately because they are separate purchases.
Use care instructions or a suitable measured sample for shrinkage. If material has already been prepared and measured afterwards, enter zero to avoid counting shrinkage twice. Calculations retain fractional measurements. Displayed dimensions are rounded to three decimal places.
Patterned cloth needs a separate placement check
The optional pattern-placement field adds your chosen extra length to every cutting row. It does not calculate a repeat, centre motifs or match neighbouring panels. Enter an allowance only after checking the actual pattern and cut positions. General reserve is not proof that a pattern will match.
All pieces keep their height along the roll. If you need the same motif at the top of several blinds, matching across vertical seams, or a half-drop repeat, draw the actual pieces on a repeat plan before ordering. The displayed row layout is only a material arrangement.
Common questions
Can I use this for relaxed or hobbled Roman shades?
No. Those shapes need different length and fold allowances. Sailrite's Roman shade project guide illustrates why the construction should be chosen before calculating material. This tool covers the flat panel model described above.
Does this include blackout lining or interlining?
You may enter a separate lining that suits the chosen construction, but its coating, washing instructions and sewing method still need checking. Interlining, bonded layers, top-setback constructions and separate sewn-on pocket strips are not modelled. Do not assume they share the same cut dimensions as ordinary lining.
Can I buy in yards?
Yes. Measurement units and purchase units are separate. Changing the measurement unit converts all dimensions, including the hidden allowance fields. Changing the purchase unit converts prices and resets the increment to 0.1 m or 0.25 yd. Confirm that increment with both suppliers before ordering.
What else belongs on my shopping list?
The result covers the two fabrics only. Your chosen system may also need a headrail, bottom bar, rods, pocket tape, hook-and-loop tape, thread and approved operating components. Use the system manufacturer's assembly and child-safety instructions. Fabric quantity alone does not check the installed blind or its operating mechanism.
Which calculator should I use for other textiles?
Use the curtain fabric calculator for gathered curtains and the cushion cover fabric calculator for flat decorative cushion covers. Each uses a different cutting model.
